So you’ve got all your figures in order and completed your tax return. You check your calculation and finally press the big Submit button… only to be met with an error,
“Authentication Failure. The supplied user credentials failed validation for the requested service.”
Error 1046
Common Causes
There are a few reasons why you might get this error:
- Your HMRC username and password are wrong
You need a (usually 12-digit) Government Gateway username and the associated password. This is different from your UTR.
You can check these by signing into your Personal Tax Account (select Sign in With Government Gateway) - You haven’t activated your account for self-assessment
When you sign up for self-assessment, HMRC will post you an activation code. You need to enter this in your Personal Tax Account to be able to send your tax return – either through CalCal or through HMRC.
Follow the instructions on your letter from HMRC to activate your account. - Your UTR is wrong
Your tax return is submitted by CalCal for you to HMRC against your UTR (universal taxpayer reference).
If you’ve entered this in CalCal incorrectly, HMRC will reject the submission immediately because your Government Gateway account is “not authorised” to send a tax return for that UTR.
Check your UTR matches the one displayed in your Personal Tax Account (logging in with the same Gov Gateway ID)
Different problem: “Connect to HMRC” or authorization failed
This is not Error 1046. When you Connect to HMRC for MTD, VAT, or importing SA pre-population, CalCal opens the HMRC website and brings you back afterward. You may see:
- “Completing HMRC authorization…” then “HMRC authorization complete” — success
- “Failed to complete HMRC authorization” or “Unable to complete authorization…” — try again from Menu → Tax or VAT → Connect to HMRC
Tips: stay logged into CalCal, complete the HMRC sign-in without closing the app, and try again within a few minutes if it fails. Pop-up blockers on web can interrupt the return to CalCal.
See also: MTD for Self Assessment, VAT MTD, Legacy Self Assessment.
When to contact support
Contact support if credentials and UTR are verified on gov.uk but Error 1046 persists, or if Connect to HMRC fails repeatedly on the same device and browser.