A myDATA integration rarely fails on the happy path — one document, one approval. It fails when the obvious points were not agreed before anyone wrote code: which documents are sent, from which system, what happens on rejection and who watches the pending list.
This is a practical checklist before implementation. It complements the technical myDATA integration guide and the integrations, myDATA and payments service. For obligations and deadlines, your accountant and the official tax-authority announcements are the source.
1. Map the documents
List which documents the business issues today and from where: commercial software, an online store, paper, spreadsheets. For each one note the type, numbering series, VAT and whether it is cancelled or credited. If that sheet does not exist, the implementation will discover it expensively, mid-transmission.
2. Who owns the truth
One system must own the document before it is sent. If the same invoice can be issued at the till and in the shop without a shared identifier, you will get duplicates. Define a stable internal identifier per document before you discuss APIs.
3. A real sandbox
Ask for separate sandbox and production credentials. Going live should not be a code change. Test issuing, cancellation, a wrong VAT number and a network drop — not only “I send one and it passes”.
4. A queue, not a wait at the till
Transmission happens after the document is issued locally. The customer at the till does not wait for the tax platform. If someone proposes a synchronous call inside the payment flow, ask in writing what happens when the service is slow or down for two hours.
5. Rejections a human can see
Every rejection needs a screen, not only a log file. Staff must be able to correct a VAT number or amounts and resubmit without a developer. If that is missing, the “automatic” integration becomes afternoon manual labour.
6. Accountant and engineer at the same table
The engineer designs queues and retries. The accountant defines classifications, exceptions and what counts as a correct document. One meeting at the start saves weeks of correction. Do not expect the software team to interpret the law in the accountant’s place.
7. Operations after handover
Ask who is alerted if transmission stops, where the exchange history is stored and whether you can export what was sent and when. Without those, you cannot answer your accountant or an audit.
If you already have an integration and the answers are vague, a focused technical review usually costs less than a month of manual corrections.
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