Custom Acumulus integration development
Appfront builds custom Acumulus integrations that fully automate your sales and invoicing, whether from your webshop, CRM or own application. Through the Acumulus API, we write sales invoices automatically, synchronise customers and products, and handle VAT correctly, including OSS for EU sales. You save manual work on every order and keep your bookkeeping up to date at all times.
What is an Acumulus integration?
Acumulus is a Dutch online accounting and invoicing platform popular with freelancers, SMEs and webshops. It is strong in e-commerce and VAT handling: it processes high transaction volumes, applies OSS VAT correctly for sales within the EU, and connects to a wide range of webshop integrations. Where manual entry becomes error-prone and time-consuming, an integration takes that work over.
In practice, a custom integration means creating sales invoices programmatically based on orders from your webshop or own software, synchronising customers and contacts, keeping products aligned with your range, and having VAT, including OSS, processed correctly and automatically. We can also pull financial data from Acumulus to feed dashboards and reports.
Appfront builds in line with the official Acumulus API documentation and the OWASP ASVS security standard. We align the mapping of invoices, customers and products with your actual bookkeeping, so the integration keeps running reliably, even when order volumes rise sharply during peak periods.
Sales invoices posted automatically
Orders from your webshop or custom software are written to Acumulus as sales invoices, with the correct customer, lines and VAT rates. No more manual retyping and no missed orders, even during busy periods.
Financial data for dashboards
Pull revenue, outstanding items and VAT figures from Acumulus to feed your dashboards and reports. Your team works with up-to-date figures without manual exports, and your data stays consistent in one place.
VAT and OSS handled correctly
The right VAT treatment for each order: domestic, EU sales via OSS, or reverse charge. The integration applies the rules consistently, so your returns are accurate and you don't have to make manual corrections.
Our development process for Acumulus integrations
We work to a proven methodology that removes uncertainty early and delivers a stable integration. From an initial analysis of your sales channels, invoicing and VAT position through to go-live and ongoing management, every step is aimed at an integration your team can understand and trust.
We map out which sales channels you're connecting, how orders should be translated into sales invoices, which customer and product data need to be included, and which VAT scenarios, including OSS, apply.
We design the integration architecture, choose the right authentication and draw up an error-handling strategy.
Implementation with automated tests, structured logging and monitoring. You see working builds along the way.
Controlled go-live with data validation and a safety net, followed by ongoing management and further development.
What an Acumulus integration delivers in practice
Every Acumulus integration is set up specifically for your sales channels, invoicing workflows and VAT position. Below are the features we most often deliver for freelancers, SMEs and webshops that use Acumulus at the heart of their bookkeeping.
Webshop sales invoices to Acumulus
Orders from WooCommerce, Shopify, Magento or your own webshop are automatically booked in Acumulus as sales invoices, with the correct customer, invoice lines, payment status and VAT rates. Hundreds of orders a day, without retyping.
Synchronising customers and contacts
Customer details from your webshop or CRM stay aligned with the customer records in Acumulus. New customers are created, existing records are updated and duplicates are prevented, so invoices always link to the right customer.
Synchronising products
Keep your product list in Acumulus aligned with the range in your webshop or stock system. Items, prices and VAT rates stay consistent, so invoice lines are always correct and product-level reports are reliable.
VAT and OSS handled correctly
The correct VAT treatment per order: domestic VAT, OSS for sales to consumers in other EU countries, or reverse charge for business customers. The rules are applied consistently, so your VAT return matches and corrections afterwards are unnecessary.
Financial data for dashboards
Pull revenue, outstanding items, payment statuses and VAT figures from Acumulus via the API and use them to feed your own dashboards and reports. Your team steers by up-to-date figures, without manual exports or loose spreadsheets.
Invoice PDFs and automatic sending
Let Acumulus generate the invoice PDF and automatically email it to the customer straight after the order is booked. No separate sending step, and every customer receives a correct invoice on time with the proper VAT breakdown.
Typical use cases in practice
An Acumulus integration looks different for every organisation. We see a number of patterns recur, and for each we have a working setup that pays close attention to the mapping of invoices, customers and products, and to correct VAT handling.
Sole traders
Self-employed professionals who want to keep their invoicing and VAT as light as possible. Sales invoices from their own tool or webshop flow into Acumulus automatically, VAT is handled correctly and the bookkeeping stays up to date without manual work. See also our API integrations.
SMEs
Growing businesses that want to automate their sales and invoicing process. Acumulus is connected to your CRM, point-of-sale system or own software, customers and products stay synchronised, and your team works with financial data from a single source. See also our Moneybird integration.
Webshops & e-commerce
Webshops with high order volumes and VAT complexity, including sales within the EU. Orders are recorded as sales invoices, OSS VAT is applied correctly and payment statuses are kept in sync. Combine with a Shopify integration or Sendcloud integration for shipping.
Accountancy firms
Accountancy firms managing the books of multiple clients in Acumulus. A separate API token and integration per administration, automated import of sales invoices and relations, and financial data ready for reporting. You may also want to compare this with our e-Boekhouden integration.
Technology we use
We build Acumulus integrations using the official Acumulus API (XML/REST over HTTPS), combined with the backend stack that suits you. The exact choice depends on your sales channels and VAT situation, so your own team can manage or further develop the implementation.
Why choose Appfront for your Acumulus integration?
Appfront has extensive experience building API integrations for a wide range of organisations in the Netherlands. We always start with a thorough analysis of your existing systems and processes. An integration should not only work technically, but also add practical value to your bookkeeping and way of working.
For every integration, we write clear documentation and make sure your own team, or any future supplier, can understand and manage it. No black box, just transparent code and clear agreements on monitoring, alerting and maintenance.
You work with a dedicated point of contact who understands both the technical and the functional side. This keeps communication short, prevents misunderstandings and speeds up decisions when choices need to be made during development.
See also our wider services around API integrations, middleware, custom software development and web app development.
- Experience with the Acumulus API and its endpoints for invoices, customers and products
- Specialists in webshop integrations (WooCommerce, Shopify, Magento)
- Familiar with VAT processing, including OSS for EU sales
- Secure by default: API token rotation, HTTPS, permissions scoped per administration
- Structured error handling and retry mechanisms
- Comprehensive logging and monitoring from day one
- Clear documentation your team can read and manage
- A fixed point of contact, no account managers passed around
- Ongoing maintenance and proactive further development
- A way of working aligned with your existing IT landscape
Security and privacy in Acumulus integrations
An Acumulus integration processes financial data and personal data of your customers: revenue, invoices, relations and VAT data. Appfront builds to the OWASP ASVS. This means, among other things: API tokens stored in secure vaults, traffic exclusively over HTTPS, scoped permissions per administration, and regular audits of the invoice and relation flows.
We document the data flows, the mapping of invoices, customers and products, and the VAT processing, so that your record of processing activities is complete and you can demonstrate compliance with the GDPR. Data is only exchanged where necessary for the administration, in line with the principle of data minimisation.
More on our security approach: information security policy and CVD policy.
- GDPR-compliant data processing and data minimisation
- Encryption in transit (TLS 1.2+) and at rest
- Role-based access and least-privilege principles
- Audit logs with traceable data flows
- Automatic retries and dead-letter queues
- Monitoring and alerting for anomalies
- Secrets management in line with best practice
- Documentation for your record of processing activities
Frequently asked questions about Acumulus integrations
Answers to the questions we are asked most often about Acumulus integrations.
An Acumulus integration is a technical link between Acumulus and another system, such as your web shop, CRM, point-of-sale system or custom application. Via the Acumulus API, sales invoices are created programmatically, customers and products are synchronised and VAT is processed correctly. An integration can be simple (writing orders from one web shop to Acumulus as sales invoices) or extensive (multiple channels, OSS VAT for EU sales, customer sync and retrieving financial data for dashboards).
Acumulus suits freelancers, SMEs and webshops with many transactions and complex VAT requirements. The platform is strong in e-commerce and VAT handling, including OSS for sales within the EU, and offers many webshop integrations. For accountant-driven workflows, Yuki or e-Boekhouden are also common choices. In an intake meeting, we can look together at which package best fits your bookkeeping.
A simple integration, such as writing orders from one webshop to Acumulus as sales invoices, can usually be delivered faster than an integration with multiple sales channels, OSS VAT for EU sales, relation and product sync, and financial data for dashboards. The timeframe depends on the number of systems and the complexity of your VAT situation. After an intake meeting, we will give you a realistic estimate.
We work with the official Acumulus API (XML/REST over HTTPS) and connect it to the backend stack that suits you, whether Node.js, Python or PHP. Authentication runs via an API token and username per administration. We use the endpoints for invoices, relations and products, and process VAT including OSS. For webshops, we connect to WooCommerce, Shopify or Magento connectors.
Costs are determined by the complexity of the data flows, the number of sales channels to connect, the desired synchronisation frequency and the amount of custom work in the VAT and business logic. Ongoing management, monitoring and support also affect the total investment. We always provide a clear quote following a no-obligation analysis of your situation.
Yes. An Acumulus integration processes financial and personal data, so Appfront builds to the OWASP ASVS: API tokens stored in secure vaults, traffic exclusively over HTTPS, scoped rights per administration and strictly separated permissions per integration. We document the data flows so your record of processing activities stays complete and you can demonstrably comply with the GDPR.
Yes. Appfront regularly takes over existing Acumulus integrations, even if they were originally set up by another party. We review the API integration, the mapping of invoices, contacts and products, the VAT processing and the error handling, document the current setup and propose improvements. From that point on, we handle changes, extensions and monitoring, including timely rotation of API tokens.
Acumulus suits sole traders, SMEs, webshops and accounting firms that want to automate their sales, invoicing and VAT administration. Typical situations include a webshop that must write large numbers of orders to sales invoices daily, a business with EU sales that wants to process OSS VAT correctly, or an accounting firm managing the administrations of several clients. For workflows that are strongly accountant-driven, we will look with you at whether Yuki or e-Boekhouden is a better fit.
Ready to build your Acumulus integration?
Tell us which sales channels you want to connect and what your VAT situation looks like. We are happy to help with sales invoices, contact and product sync, OSS processing and financial data for dashboards. A no-obligation first conversation will give you a clear picture of the possibilities within half an hour.