Validate a customer's tax ID before applying reverse charge using the Quaderno tax ID validation endpoint
domain: developers.quaderno.io · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Send a GET request to the tax ID validation endpoint with country and tax_id query parameters, authenticated with your Quaderno API key via HTTP Basic Auth
Use the tax_id parameter rather than the deprecated vat_number parameter; the legacy taxes/validate endpoint has been removed entirely in favor of tax_ids/validate
Read the boolean response: a value of true confirms the tax ID is valid and belongs to an actual business
If the response is null rather than true or false, treat it as a safeguard case and do not apply reverse charge for that transaction
Check Quaderno's status page for tax-ID-validation-related incidents if validations fail unexpectedly, since the endpoint depends on external government validator services with their own maintenance windows
Known gotchas
Quaderno validates tax IDs only for the EU, UK, Switzerland, Quebec (Canada), Australia, and New Zealand; other countries are not supported by this endpoint
A null response is not the same as an invalid (false) tax ID; treat null as could-not-verify and withhold reverse charge rather than treating it as a hard failure
Sending the old vat_number parameter or calling the removed taxes/validate path will fail; migrate to tax_id and tax_ids/validate
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