Hi info1789, thanks for joining this thread. This error is one of the most common issues encountered when using MTD services in QuickBooks Online. This message may appear if:

- You need to reauthorise the connection between QuickBooks Online and HMRC (reauthorisation is required every 18 months) 
- You haven't entered the correct credentials for MTD provided by HMRC when setting up MTD in QuickBooks.
- The VAT registration number in QuickBooks doesn't match HMRC's records. If you've been issued a new VAT registration number, you'll need to update this in your VAT settings.

We'll send an email when its time to re-authorise. If you haven't received this, you can still re-authorise by disconnecting MTD in your account (click the Cog > Account & settings > Advanced > Making tax digital > Select Learn how to disconnect and follow the steps). Once complete, refresh the page and select Learn how to connect.