Welcome back to the QuickBooks Community, Frances w. This isn't the kind of feeling that I'd wish you to have when submitting CIS returns. With this, let me share additional details about rejecting a return. Then, ensure you'll be routed to the right person to assist you further on this matter.

As mentioned by my colleague, there are slight causes why HMRC might reject your return. Please see the list of things to check before you attempt to file a return again:

• You may be using the wrong login details. Log into the HMRC website to confirm that your Government Gateway user ID and password are correct.
• Make sure you're using the right 10-digit Unique Taxpayer Reference (UTR) number.
• Review that you're using the correct PAYE Reference number.
• Check that your suppliers have the correct references and CIS setup:
  • Accounts Office reference number
  • Subcontractor UTR number
  • National Insurance (NI) number
  • Verification number
• Delete any special characters and additional spaces in the subcontractor/contractor name field. Only use letters A-Z and numbers 0-9.

If you still encounter the same issue after checking the details documented above, I recommend contacting our QuickBooks Online Support Team. They have the tools to pull up your account in a secure environment and deeply investigate the cause of the issue. 

Lastly, you may refer to this article to see steps on how you can unfiled a CIS return if you need to make changes to an already closed period: How to unfile a CIS return in QuickBooks Online. 

Please keep in touch if there's anything else I can do to help you succeed with your CIS return. I've got your back. Have a great day and be safe.