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HMRC error messages · Income Tax

FORMAT_NINO

The National Insurance number sent is not in a valid format: two letters, six numbers and a final letter from A to D, with some letter combinations never issued.

HMRC's message · HTTP 400
The NINO format is invalid

When it appears

Any income tax request, which always carries the client's National Insurance number.

What to check

  • There are no spaces or stray characters in the number on the client's record.
  • The first two letters are a combination HMRC issues (for example, it never issues numbers starting BG, GB, NK, KN, TN, NT or ZZ).
  • The last letter is A, B, C or D.

How to fix it

Correct the number on the client's record. If you are unsure of it, ask the client to check their payslip, P60 or HMRC app.

Making Tax Digital in Accountin

Accountin shows HMRC's code and message next to a plain explanation, and keeps HMRC's reply against every submission.

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