SERIES_FORMAT_INVALID_CHARACTERS

When it happens

The numbers the series would generate contain a character the AEAT does not accept in an invoice number: only printable ASCII is allowed, except ", ', <, > and =.

How to fix it

Remove those characters from the code or the format.

Retry

Not as is: the same request fails the same way. Fix the cause described above, then send the request again, under a new Idempotency-Key if the body changed.

Returned by

The operations where this code is most likely. The list is not exhaustive.

• POST /v1/companies/{company_id}/series
• PATCH /v1/companies/{company_id}/series/{series_id}

Rules that cite this code

• NUM-008 An invoice number fits AEAT's length and character set

Example response

When this error occurs, the API answers 422 Unprocessable Content with a JSON body of this shape:

{
  "type": "https://docs.beel.es/errors/SERIES_FORMAT_INVALID_CHARACTERS",
  "title": "SERIES_FORMAT_INVALID_CHARACTERS",
  "detail": "The number this series generates would contain characters the AEAT does not accept: ‹value›. Use printable ASCII characters only, without quotes, <, > or =",
  "instance": "/v1/<resource>",
  "errors": [],
  "success": false,
  "error": {
    "code": "SERIES_FORMAT_INVALID_CHARACTERS",
    "message": "The number this series generates would contain characters the AEAT does not accept: ‹value›. Use printable ASCII characters only, without quotes, <, > or =",
    "details": {}
  },
  "meta": {
    "timestamp": "2026-05-21T10:00:00Z",
    "request_id": "4bf92f3577b34da6a3ce929d0e0e4736"
  }
}

The type URI is stable and always resolves to this page.

Message

Send the request with Accept-Language: <es|en|ca> to receive the message in your preferred language.

Placeholders like ‹value› are filled in at runtime with the actual values of your request.

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