Accounts receivable automation software helps businesses streamline the process of collecting payments from customers, managing invoices, tracking outstanding balances, reconciling incoming payments, and reducing overdue receivables. For Indian businesses dealing with multiple customers, payment terms, GST-compliant invoices, and different banking channels, these platforms can significantly improve cash flow visibility and reduce the administrative burden on finance teams.
Modern accounts receivable solutions combine invoice delivery, automated payment reminders, customer payment portals, receivables reporting, cash application, dispute management, and integration with accounting or enterprise resource planning systems. More advanced platforms also use artificial intelligence, machine learning, and payment data to identify collection risks, predict payment behaviour, and help finance professionals prioritise accounts that require immediate attention.
In India, the right software depends on the organisation’s size, customer base, billing complexity, existing accounting systems, and collection processes. Small businesses may need straightforward invoicing and payment tracking, while large enterprises often require automated cash application, multi-entity support, customer credit management, and sophisticated collection workflows.
The following software platforms offer different capabilities for managing accounts receivable, from comprehensive order-to-cash automation to integrated accounting and payment collection tools. Their features, deployment models, and suitability vary, making it important to evaluate each platform against the organisation’s operational requirements.
1. HighRadius
HighRadius is an accounts receivable automation and order-to-cash management platform designed primarily for mid-sized and large enterprises that handle substantial invoice volumes, complex customer relationships, and multiple payment channels. Its receivables management capabilities cover collections, cash application, credit management, electronic invoicing and payment processing, deductions management, and accounts receivable analytics. The platform is particularly relevant to organisations seeking to move beyond basic invoice tracking towards a connected, data-driven finance operation.
One of its core capabilities is automated collections management. Finance teams can organise customer accounts according to overdue balances, payment histories, risk indicators, and collection priorities. The software helps assign accounts to collectors, schedule follow-ups, generate reminders, and maintain records of customer communications. By consolidating outstanding invoices and collection activities into a common workspace, it allows finance managers to identify which accounts require immediate intervention and which can be handled through automated communication.
HighRadius also offers automated cash application, a function that matches incoming customer payments with the corresponding invoices and outstanding balances. In conventional finance departments, this task can involve reviewing bank statements, identifying payment references, interpreting remittance information, and manually updating accounting records. Automated matching can reduce repetitive data entry, while exception-handling workflows help employees investigate payments that cannot be confidently matched.
The platform’s artificial intelligence capabilities support the interpretation of remittance data, payment matching, collection prioritisation, and the identification of unusual account activity. Its deductions management functionality helps organisations investigate short payments, pricing discrepancies, missing documentation, and other reasons customers may withhold part of an invoice amount. These issues can be assigned to appropriate teams and tracked until resolution, creating a more organised approach to recovering disputed amounts.
Credit management is another important component. Businesses can use customer financial information, payment history, credit assessments, and internal policies to support credit decisions. This is particularly useful for companies that sell on credit to distributors, retailers, wholesalers, or other business customers. Integrated analytics provide visibility into overdue receivables, collection performance, and broader cash flow trends.
HighRadius is most suitable for enterprises that need extensive automation across the entire receivables lifecycle. Implementation requires careful integration with existing enterprise resource planning systems, customer records, banking information, and finance processes. Businesses should assess implementation complexity, licensing costs, regional support, and the availability of integrations with their current systems before adopting the platform.
2. Zoho Books
Zoho Books is a cloud-based accounting and invoicing platform suitable for Indian small and medium-sized businesses, professional service providers, consultants, agencies, wholesalers, and growing companies. Its accounts receivable capabilities are integrated into a broader accounting system, allowing businesses to create invoices, record payments, track outstanding balances, and manage customer transactions without purchasing a separate enterprise-grade receivables platform.
A key feature is invoice management. Businesses can create customer invoices, configure payment terms, establish recurring invoices where appropriate, and monitor whether payments have been received. Invoice templates can be customised with business details, branding, and relevant transaction information. Automated reminders help finance teams follow up on unpaid invoices without manually drafting individual messages for every customer.
The platform supports GST-oriented accounting workflows relevant to Indian businesses. Depending on the applicable plan and configuration, users can manage tax information, generate GST-compliant invoices, and work with supported e-invoicing and other statutory workflows. Companies should confirm current applicability, integration requirements, and plan-specific limitations before relying on any feature for regulatory compliance.
Zoho Books also provides customer account records, accounts receivable reports, payment tracking, and bank reconciliation capabilities. Finance teams can examine unpaid invoices, ageing balances, customer transaction histories, and payments that require reconciliation. These reports help identify customers who regularly pay late and provide a clearer picture of the business’s outstanding working capital.
Integration with other business applications within the Zoho ecosystem can further reduce repetitive work. Depending on the configuration, businesses may connect accounting with customer relationship management, subscription billing, inventory, expense management, and other operational systems. Such integration can help ensure that customer details and financial transactions remain consistent across departments.
For service businesses, recurring billing and organised customer records can be particularly useful. For distributors and trading companies, invoice tracking and receivables reporting can simplify follow-ups across a large customer base. The cloud-based interface also supports access to financial information without requiring the entire accounting team to work from one physical location.
Zoho Books is a practical option for businesses that want receivables automation as part of everyday accounting rather than a standalone enterprise system. However, organisations with highly complex deductions, large-scale remittance matching, sophisticated credit risk models, or extensive multinational collection operations may need additional applications or integrations. Pricing, user limits, automation availability, and advanced features vary by subscription plan.
3. SAP S/4HANA Finance
SAP S/4HANA Finance is an enterprise financial management solution that supports accounts receivable as part of a broader system for accounting, financial operations, reporting, and business process management. It is designed for organisations with complex operational structures, including large manufacturers, multinational corporations, consumer goods companies, infrastructure businesses, and enterprises operating across multiple legal entities.
Its accounts receivable capabilities include customer accounting, invoice processing, payment recording, open-item management, reconciliation, and receivables reporting. By connecting financial transactions with wider enterprise processes, SAP can provide finance departments with a consistent view of customer balances, billing activity, and payment status. This is particularly valuable where invoices originate from multiple business units, sales channels, or operational systems.
SAP supports the management of open customer items and incoming payments. Finance teams can use configured matching and clearing processes to connect receipts with outstanding invoices. Where payment references are incomplete or amounts do not match, exceptions can be reviewed through established accounting workflows. Depending on the implementation, additional automation tools can improve the handling of bank statements, remittance information, and payment allocation.
Credit management and customer risk controls can also form part of the wider SAP environment. Organisations can establish credit limits, assess exposure, monitor overdue balances, and apply internal policies to customer accounts. These controls are useful for businesses that need to balance sales growth with the risk of delayed payments or bad debts.
Another important strength is integration with order management, billing, sales, procurement, and financial reporting. For example, finance teams can investigate whether an overdue invoice relates to a billing error, a delivery issue, a customer dispute, or a payment delay. Access to connected operational information can reduce the need to request documents from multiple departments before responding to a customer.
SAP’s reporting capabilities support analysis of receivables ageing, customer balances, overdue accounts, and financial performance. Organisations can use configured dashboards and reporting tools to monitor collection effectiveness and identify potential problems across business units. The overall value depends on the quality of master data, system configuration, and the consistency of internal procedures.
SAP S/4HANA Finance is best suited to enterprises that need receivables management embedded within their core financial infrastructure. It is generally more demanding to implement than a small-business accounting application and may require specialist consultants, structured change management, and integration planning. Companies should also distinguish between core SAP receivables functionality and additional products or licences needed for more advanced automation.
4. Oracle NetSuite
Oracle NetSuite is a cloud-based enterprise resource planning platform that combines accounting, financial management, customer transactions, inventory, order management, and other business functions. Its accounts receivable capabilities are integrated into the financial management environment, making it suitable for growing businesses and established enterprises that need consistent visibility across billing, payments, and outstanding customer balances.
The platform supports invoice creation, payment recording, customer account management, receivables ageing, and financial reporting. Businesses can maintain customer records and payment terms while monitoring outstanding balances and overdue invoices. Because receivables information sits within the broader ERP environment, finance teams can connect billing and collection activity with sales transactions, fulfilment processes, and financial results.
NetSuite’s invoice management capabilities can support organisations with recurring billing, multiple customer categories, and complex transaction volumes. Automated workflows can be configured to reduce repetitive tasks, enforce internal approval procedures, and standardise how invoices and customer balances are handled. Depending on the implementation, integrations can also connect billing activity with payment gateways and other systems used to collect customer payments.
Payment reconciliation is another important consideration. Incoming receipts must be linked to the correct customer accounts and invoices, and unresolved differences must be investigated before financial records can be finalised. NetSuite provides accounting and reconciliation functionality, while the extent of automated matching depends on the transaction structure, available bank feeds, configuration, and any additional applications used.
The platform also provides financial reporting tools that help management review outstanding receivables, customer balances, collection trends, and working capital. Multi-subsidiary and multi-currency capabilities can be valuable for companies operating across different markets, subject to the relevant modules and configuration. These features are particularly useful for businesses expanding beyond a single legal entity or domestic market.
NetSuite can help consolidate finance operations that previously relied on disconnected accounting software, spreadsheets, and separate billing systems. Its centralised data model can reduce duplicate records and improve the consistency of financial reporting, provided that data migration and system governance are handled properly.
The platform is appropriate for growing businesses that require more than basic invoicing and anticipate increasing complexity in their operations. It may be excessive for a small business that only needs invoices and payment reminders. Prospective users should evaluate implementation costs, subscription pricing, customisation requirements, local tax workflows, and the availability of specialised cash application or collections automation features.
5. Microsoft Dynamics 365 Finance
Microsoft Dynamics 365 Finance is an enterprise financial management solution that helps organisations manage accounting, customer balances, collections, credit policies, and financial reporting. It is particularly relevant to medium-sized and large businesses that require structured finance workflows and integration with other Microsoft business applications.
The accounts receivable functionality supports customer invoicing, payment processing, settlement of outstanding transactions, and monitoring of overdue balances. Finance teams can maintain customer payment terms, establish collection procedures, and review outstanding invoices through customer account records. These features help organisations standardise receivables processes across business units and maintain consistent financial information.
Collections management is an important part of the system. Businesses can configure collection activities, generate customer statements, identify overdue accounts, and organise follow-up procedures. Collection letters and reminders can be managed through supported workflows, allowing finance teams to reduce the amount of time spent manually preparing routine communications. The precise automation available depends on the configuration and the additional services connected to the finance environment.
The platform also supports credit management processes. Organisations can establish customer credit limits, review outstanding exposure, and use credit controls to help manage the risk associated with selling on credit. These capabilities are valuable for distributors, manufacturers, and B2B service providers that handle substantial receivables portfolios.
Payment settlement and reconciliation help finance teams connect incoming receipts with outstanding invoices. Businesses can configure bank integration and matching processes to improve the recording of customer payments. More complicated transactions, including partial payments, deductions, and payments covering multiple invoices, may require additional configuration or manual review.
Microsoft Dynamics 365 Finance can also be integrated with the wider Microsoft ecosystem. Depending on the organisation’s setup, this may include reporting through Power BI, workflow automation through Power Automate, and collaboration through Microsoft Teams. Such integration can make financial information easier to share across finance, sales, and customer service departments.
Reporting features help businesses monitor overdue balances, collection performance, customer exposure, and broader financial trends. Management can use these insights to review payment behaviour, assess the effectiveness of collection strategies, and identify accounts that require additional attention.
For Indian businesses, implementation planning should cover GST requirements, local banking integrations, invoice formats, and applicable statutory reporting. These capabilities should be verified against the proposed deployment rather than assumed to be available automatically in every configuration.
Microsoft Dynamics 365 Finance is a strong option for enterprises seeking integrated financial management and structured receivables operations. Its implementation can require significant configuration, data preparation, and employee training. Businesses should determine whether native functionality meets their requirements or whether additional collections, payment, or cash application applications are necessary.
6. Billtrust
Billtrust is a specialised B2B accounts receivable automation platform designed to help businesses manage invoicing, customer payments, collections, credit processes, and cash application. It is particularly relevant to manufacturers, distributors, transportation businesses, healthcare suppliers, and other organisations that invoice business customers regularly and manage substantial receivables volumes.
A central feature of Billtrust is electronic invoice delivery. Businesses can deliver invoices through supported digital channels and customer accounts payable portals, reducing dependence on manual document distribution. The platform is designed to help suppliers manage the administrative requirements associated with delivering invoices to multiple business customers, each of which may follow different invoice submission procedures.
Billtrust also supports electronic payments and customer payment experiences. Depending on the implementation, customers can access payment information, review invoices, and use supported payment methods. Making payment information easier to access can reduce friction in the collection process and help finance teams avoid repeated requests for invoice copies or account statements.
Cash application is another significant capability. The platform helps match incoming payments with outstanding invoices using payment data and remittance information. Automated matching can reduce manual allocation work, while unresolved items can be directed for review. This is especially useful for businesses receiving bulk payments, partial settlements, or payments accompanied by inconsistent references.
Collections automation helps finance teams organise follow-ups and prioritise overdue customer accounts. The platform can support structured communication, collection workflows, and visibility into account activity. More advanced capabilities use payment patterns and other available data to inform collection priorities and cash flow expectations.
Billtrust also offers credit management functionality, allowing businesses to support customer credit decisions and monitor financial exposure. Bringing credit, collections, invoice delivery, and cash application into a connected environment can help finance teams understand the wider customer payment cycle rather than treating each activity as a separate task.
Integration with existing ERP and accounting systems is an important part of deployment. Companies should verify that their specific financial system, banking arrangements, payment channels, and customer portals are supported. They should also establish how invoice status, payment information, and reconciliation results will synchronise with the accounting system.
For Indian businesses serving international B2B customers, Billtrust may be worth evaluating when customer portal requirements and high invoice volumes create significant administrative work. However, organisations should assess local payment support, India-specific implementation requirements, contractual terms, and the total cost of deployment before choosing the platform.
7. Quadient Accounts Receivable Automation
Quadient Accounts Receivable Automation is designed to connect invoice delivery, collections, customer payments, credit management, dispute handling, and cash application. The platform helps businesses organise the receivables process within a coordinated environment rather than relying on disconnected spreadsheets, email conversations, and manual reminders.
Invoice delivery is one of its core functions. Finance teams can manage customer communications through supported digital and traditional channels, helping ensure that invoices reach the appropriate recipients. Consistent invoice delivery is important because delayed or misdirected invoices can postpone payment even when a customer is financially capable of settling the balance.
Quadient supports automated collections workflows that allow organisations to configure reminders and follow-up activities according to customer payment terms and account status. Businesses can establish communication schedules and escalation rules so that routine collection tasks occur consistently. This can help collectors concentrate on complex overdue accounts instead of spending excessive time tracking basic follow-ups.
The platform also supports dispute management. Customer deductions, invoice disagreements, missing documentation, and other payment issues can be recorded and tracked through defined processes. Centralised dispute information can improve coordination between finance, sales, customer service, and other departments responsible for resolving payment delays.
Customer payment options are another important component. By providing supported digital payment experiences, organisations can make it easier for customers to settle invoices and review their balances. Depending on the configuration, payment information can be connected with receivables workflows to improve visibility into collection progress.
Quadient’s cash application capabilities help businesses match payments against outstanding invoices and improve reconciliation accuracy. This is particularly valuable where payment information arrives through several channels and finance teams must determine which invoices have been settled. Unmatched payments and exceptions can be investigated through controlled workflows.
The platform also incorporates AI-supported capabilities for analysing payment behaviour, prioritising collection work, and interpreting incoming customer communications. Such features can help identify emerging collection risks and reduce repetitive administrative work. Their effectiveness depends on the quality of available data, configuration, and the complexity of customer interactions.
Quadient may be suitable for medium-sized and large organisations seeking a specialised receivables solution that connects collections with invoice delivery and payment processing. Before implementation, businesses should examine ERP compatibility, local banking support, integration costs, and the availability of the specific features required for Indian operations.
8. Esker Accounts Receivable Automation
Esker provides finance automation solutions covering accounts receivable, accounts payable, and related business processes. Its accounts receivable capabilities are intended to help organisations reduce manual work throughout the order-to-cash cycle, from customer credit assessment and invoicing to collections, dispute resolution, and payment reconciliation.
One of the key components is credit management. Businesses that supply goods or services on credit need reliable procedures for evaluating customers, establishing credit limits, and monitoring exposure. Esker’s credit management capabilities can help organise credit information and standardise assessment workflows, allowing finance teams to make decisions using more consistent information.
The platform also supports electronic invoicing and invoice delivery. Automated document distribution can reduce manual effort and help businesses track invoice-related activities. For companies processing substantial volumes of B2B invoices, this can improve administrative efficiency and make it easier to investigate delayed payments caused by billing or delivery problems.
Collections management helps finance departments organise customer follow-ups and manage overdue receivables. Workflows can be configured to support reminders, collection activities, and prioritisation of accounts requiring attention. By consolidating account information, the platform can help collectors access outstanding balances and related customer information without switching repeatedly between separate systems.
Dispute management is another important feature. Businesses often experience payment delays because customers question pricing, quantities, delivery documentation, contractual terms, or invoice accuracy. Esker helps organise dispute information and coordinate resolution activities, making it easier to identify recurring issues and track responsibility for outstanding cases.
Cash application and payment reconciliation can further reduce manual finance work. These processes help connect incoming payments with invoices and customer accounts, while exceptions can be directed for further investigation. The degree of automation depends on the quality of remittance information, payment formats, and integration with existing financial systems.
Esker can be valuable for organisations looking to improve coordination between finance teams and other departments involved in customer transactions. Its wider finance automation environment may also help businesses connect receivables activities with other administrative workflows.
For Indian companies, the suitability of Esker depends on deployment requirements, local tax processes, integration with existing ERP systems, and support for relevant banking and payment channels. It is generally more appropriate for organisations with established finance processes than for very small businesses seeking only basic billing and reminders.
9. TallyPrime
TallyPrime is a widely used accounting and business management solution in India. It is particularly suitable for small and medium-sized enterprises, wholesalers, distributors, retailers, manufacturers, and service providers that want to manage customer invoices and outstanding payments alongside their regular accounting activities.
Its accounts receivable capabilities are built around customer ledgers, sales vouchers, payment entries, outstanding bills, and receivables reports. Businesses can record credit sales, maintain customer balances, track payments received, and review invoices that remain unpaid. This makes it possible to monitor receivables without maintaining separate records for every transaction in spreadsheets.
Bill-wise accounting is especially useful for businesses that sell to customers on credit. Finance staff can track outstanding bills and record settlements against individual transactions. This helps distinguish fully paid invoices from partially settled or overdue bills and provides a clearer view of customer balances.
TallyPrime also offers reports that help users examine outstanding receivables, customer account positions, and ageing information where appropriately configured. These reports can help business owners identify customers with overdue balances and determine which accounts require follow-up. For smaller businesses, this basic visibility can be a substantial improvement over manually maintained collection registers.
The software supports accounting and GST-related workflows relevant to Indian businesses. Companies can record sales transactions, maintain tax information, and generate applicable accounting reports. E-invoicing and other compliance features depend on the product version, configuration, eligibility, and applicable regulations. Businesses should confirm their statutory requirements before relying on a particular workflow.
TallyPrime’s accounting foundation is valuable because receivables do not operate independently of other financial activities. Customer payments affect bank balances, outstanding bills, and financial statements. Maintaining these records within one accounting environment can reduce duplicate data entry and improve the consistency of financial information.
However, TallyPrime should be distinguished from specialised enterprise AR automation platforms. Although it provides customer outstanding management and accounting workflows, businesses with complex automated collection campaigns, sophisticated AI-based payment matching, customer self-service portals, or extensive dispute management may need integrations or supplementary tools.
For Indian SMEs that already use TallyPrime, improving customer ledger discipline, bill-wise tracking, payment recording, and regular outstanding reports may provide a practical starting point for receivables automation. Businesses should evaluate the availability of their required integrations, payment reminders, remote access arrangements, and automation features in the specific edition they intend to use.
10. Odoo Accounting
Odoo Accounting is part of Odoo’s integrated business management platform, which combines financial management with applications for sales, customer relationship management, inventory, purchasing, invoicing, and other business functions. Its accounts receivable capabilities make it relevant to small and medium-sized businesses seeking an integrated system that can expand as operational requirements grow.
The platform supports customer invoicing, payment tracking, reconciliation, and receivables reporting. Businesses can create invoices from relevant sales transactions, monitor outstanding amounts, and record incoming payments. Connecting these activities with sales and customer records helps reduce the need to transfer information manually between separate applications.
Automated follow-up activities can help businesses manage overdue invoices. Depending on the configuration and available edition, users can establish follow-up levels, schedule reminders, and organise customer communication according to payment status. These workflows can make collection procedures more consistent and reduce the time spent manually checking which customers need to be contacted.
Odoo Accounting also provides bank reconciliation capabilities. Businesses can import or connect supported bank transaction information and match incoming payments against outstanding invoices. Automated reconciliation can simplify routine transactions, while unmatched receipts and differences can be reviewed by finance staff. The effectiveness of matching depends on the quality of transaction references and the available bank integration.
Integration with Odoo’s other applications is one of its principal advantages. A business can connect customer relationship management, sales orders, inventory, and invoicing to create a more continuous operational workflow. For example, sales teams can maintain customer information while finance teams use the associated records to manage invoices and payments.
The platform’s modular structure allows organisations to begin with accounting and add other applications as their needs develop. This can be useful for businesses that want to avoid introducing a large enterprise system all at once. Nevertheless, businesses should carefully plan application selection, access permissions, data migration, and process configuration to avoid unnecessary complexity.
For Indian businesses, local accounting and tax requirements require particular attention. GST configuration, supported e-invoicing workflows, localisation, and banking integrations should be checked against the specific Odoo version and deployment model. Companies may also need implementation partners to configure workflows and integrate external applications.
Odoo Accounting is suitable for businesses that want receivables management as part of a wider operational platform. It may not provide every advanced collection, credit risk, deduction management, or AI-driven cash application feature available in specialist enterprise software without additional configuration or complementary applications.
How to Choose the Best Accounts Receivable Automation Software in India
Choosing accounts receivable automation software requires evaluating the organisation’s current financial processes, customer payment behaviour, invoice volumes, and accounting infrastructure. A solution that works well for a small trading business may not be suitable for a multinational company with multiple subsidiaries, thousands of customer accounts, and complex payment reconciliation requirements.
Automation capabilities should be a primary consideration. Businesses should determine whether they need invoice creation, automated reminders, payment links, cash application, collection prioritisation, dispute management, or credit risk assessment. Organisations with relatively simple billing requirements may find integrated accounting software sufficient, while companies managing complex receivables portfolios may benefit from specialised platforms such as HighRadius, Billtrust, Quadient, or Esker.
Integration with existing systems is equally important. The selected software should work with the organisation’s accounting or ERP platform, customer database, banking channels, and payment providers. Businesses should clarify whether integrations are native, require third-party applications, or involve custom development. They should also establish how frequently information synchronises and how integration failures are handled.
Indian tax and payment requirements must be assessed carefully. Companies should confirm support for relevant GST workflows, applicable e-invoicing requirements, local banking arrangements, and the payment methods their customers use. Availability can differ according to the product edition, implementation partner, and deployment configuration.
Reporting and cash flow visibility can help management understand how efficiently the organisation collects payments. Useful reports include receivables ageing, overdue invoices, customer payment history, collection effectiveness, and days sales outstanding. Businesses should ensure that reports can be configured to reflect their payment terms, reporting periods, and internal performance indicators.
Security and access controls are essential because receivables systems contain customer information, transaction details, and financial records. Organisations should review role-based permissions, audit trails, data protection arrangements, backup procedures, and available security certifications. They should also determine how employee access will be managed when staff members change roles or leave the organisation.
Finally, companies should compare the total cost of ownership rather than looking only at subscription fees. Implementation, integrations, data migration, training, support, transaction charges, and additional modules can affect the overall investment. A structured demonstration using the company’s actual collection scenarios can help establish whether a platform delivers practical value.
Conclusion
Accounts receivable automation software can help Indian businesses improve invoice visibility, organise collection activities, reconcile payments, and manage outstanding customer balances more effectively. The most suitable solution depends on the scale and complexity of the organisation’s financial operations.
HighRadius, Billtrust, Quadient, and Esker offer specialised capabilities for organisations seeking broader receivables automation. SAP S/4HANA Finance, Oracle NetSuite, and Microsoft Dynamics 365 Finance provide integrated financial management for businesses with more complex operational requirements. Zoho Books, TallyPrime, and Odoo Accounting offer practical options for businesses that want customer invoicing and receivables management within a broader accounting or business management system.
Before making a decision, businesses should evaluate the specific features available in their chosen edition, integration requirements, India-specific compliance workflows, implementation costs, and scalability. The right platform should do more than record unpaid invoices: it should help finance teams identify collection priorities, reduce avoidable delays, maintain accurate records, and make better-informed working capital decisions.
