To fix this, please log in to the HMRC account and confirm whether the submission has been successfully sent on HMRC’s side:
Scenario 1 - HMRC Website confirms submission was fine. This means that the Coins system did not change the submission status from unsent to submitted, so you will need to change the status of the return via the toolbox utility, Amend VAT Return Submission.
Scenario 2 - HMRC Website did not receive the submission, get the user to cancel the return, refresh the tokens and submit again.