Thank you for sharing a screenshot, Helen. 
 

The error CLIENT_OR_AGENT_NOT_AUTHORISED indicates that QuickBooks is no longer authorized to connect to HMRC or that your credentials are incorrect. This occurs due to the following reasons:
 

• Connection to HMRC has expired (18 months)
• Incorrect credentials
• HMRC hasn't authorized your agent services account
• VAT registration number doesn't match HMRC records.
   

Since you've reconnected, confirm you're using your MTD credentials during the process. Make sure not to use general Government Gateway credentials. Refer to this article for more info: Fixing MTD (Making Tax Digital) issues in QuickBooks Online.
 

If the same error occurs, I recommend contacting our live support team. They have the resources to further verify this situation and ensure you can file your VAT returns on time.
 

Let me know in the comments below if you have further questions about this matter.