Integrating with the Dutch trade register from Germany
BillStack is a fast-growing invoicing and accounting platform based in Berlin, serving thousands of European businesses. After a successful expansion into the Dutch market, they ran into a fundamental problem: their Dutch customers had to manually enter KVK numbers and fill in company details when creating invoices.
The official KVK API proved complex and slow to integrate from outside the Netherlands. The documentation was largely in Dutch, authentication was cumbersome, and combining KVK data with VAT validation via VIES required multiple separate API calls to different systems.
The result: Dutch customers dropped off during onboarding because entering company details took too long. Invoices regularly contained errors in company names, addresses, and VAT numbers. The support team in Berlin struggled to help with Dutch business registrations they were unfamiliar with.
KVKBase API and widget in the invoicing flow
BillStack integrated the KVKBase API and widget directly into their invoicing flow. When a Dutch customer creates a new invoice recipient, they can simply enter a KVK number. All company details -- name, address, legal form, and VAT number -- are automatically filled in and validated.
The integration was surprisingly simple. Thanks to English-language documentation and a standard REST API, the BillStack team in Berlin was able to build the integration without any knowledge of the Dutch trade register. The KVKBase API combines KVK data and VIES VAT validation in a single call, eliminating the need to integrate separate systems.
const response = await fetch(
`https://api.kvkbase.nl/v2/company/${kvkNumber}`,
{
headers: {
'Authorization': `Bearer ${process.env.KVKBASE_API_KEY}`,
},
}
);
const company = await response.json();
// company.name, company.address, company.vatNumber, company.legalForm
// Everything in a single API callThe full integration -- including the frontend widget and backend API validation -- was operational within two days. The team had originally planned at least two weeks for integration with the official KVK API.
The invoicing flow transformation
Before
- Dutch customers manually entered all company details
- VAT numbers had to be validated separately via VIES
- Integration with official KVK API took weeks of development
- Invoices regularly contained incorrect addresses and names
- High drop-off rate during Dutch customer onboarding
- German support team couldn't help with KVK issues
Now with KVKBase
- Customer enters only KVK number, rest is auto-filled
- VAT validation automatic via VIES in the same call
- Integration completed in 2 days
- Invoices are always correct and complete
- Dutch customer onboarding conversion up 40%
- English API docs, no Dutch knowledge required
Measurable impact from day one
The results were immediately visible. Dutch customers who previously dropped off during onboarding now completed the process in a fraction of the time. Manual data entry errors dropped dramatically, and the support team in Berlin received virtually no more tickets about incorrect company details on invoices.
Company details are automatically retrieved and filled in based on the KVK number. Dutch customers only need to enter this single number when creating an invoice recipient.
The full integration was operational within two days, including the frontend widget and backend API validation. With the official KVK API, the team would have needed at least two weeks.
Thanks to automatic VIES validation with every lookup, VAT errors on invoices have been completely eliminated. This saves manual correction work and prevents issues with tax filings.
Dutch customers now complete onboarding 40% faster. Fewer fields to fill in means less friction, and that translates directly into higher conversion.
"As a German company, integrating with the Dutch Chamber of Commerce registry was a nightmare. KVKBase made it as simple as a REST call."
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