Tax return submission errors

Occasionally, there may be an error at the point of tax return submission. We know this can be unsettling, but it’s usually easily explained and can be fixed.

If your HMRC credentials are wrong, you will see:

Authentication Failure. The supplied user credentials failed validation for the requested service.

You should be able to fix this quickly by yourself:

  1. Double-check your Government Gateway password (and ID). For example, try logging into your HMRC Online Account and resetting your password if necessary.
  2. If it’s your first time doing your own tax return, check your HMRC Online Account. You should see a box called 'Self Assessment'. If not, follow the instructions at the top of the page to 'Add a tax to your account'.

If you’ve already submitted a tax return for the year, you may see:

A submission for the user and tax year has already been successfully made. If amendment(s) are required, you must make an amended submission.

To resolve this or any issue not covered here, please raise a support ticket:

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