HMRC's message · HTTP 400
You are outside the amendment window
When it appears
Amending a final declaration, calculation or annual submission after HMRC's deadline for changes.
What to check
- The tax year concerned and today's date.
How to fix it
Make the correction through HMRC's normal amendment or overpayment relief route for that year.
Making Tax Digital in Accountin
Accountin will send VAT returns and income tax updates to HMRC once HMRC grants it live access. It then shows HMRC's code and message next to a plain explanation, and keeps HMRC's reply against every submission.