> For the complete documentation index, see [llms.txt](https://amast-einvoice.gitbook.io/amast-einvoice-sass/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://amast-einvoice.gitbook.io/amast-einvoice-sass/best-practises.md).

# Best Practises

## Do

* Use a unique `idempotency-key` per logical submit; reuse only for identical retries.
* Store `submissionBatchId` and `documentId` from submit responses.
* Handle `402` by topping up credits before retrying.
* Rotate API keys if exposed; separate keys per environment.
* Validate buyer TIN + ID at **customer create/update**, cache results.
* For credit notes on external invoices, always send `relatedInvoice.referenceId` and `relatedInvoice.lhdnUuid`.
* Use a new `referenceId` for each credit note.
* Align amounts and tax with LHDN rules before production.

## Don't

* Reuse an idempotency key with a different body.
* Send more than 100 documents per submit.
* Put API keys in browsers, mobile apps, or public repos.
* Tight-loop retries without reading error bodies.
* Assume we block duplicates on MyInvois or other systems.
* Omit `lhdnUuid` for credit notes when the parent was issued outside this platform (unless `"NA"` applies).
* Reuse the same `credit_note` + `referenceId` while a prior CN is in-flight or LHDN Submitted/Valid.
* Call Validate TIN on every submit.


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