HMRC's message · HTTP 400
Invalid period key
When it appears
Submitting or viewing a VAT return.
What to check
- That the return was prepared from the obligation HMRC returned, and the key was not typed in.
How to fix it
Refresh the client's VAT obligations and prepare the return from the open one.
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.