QB Issue Resolution:

First you will want to remove the linked Bill Payment by deleting it, and then you will be able to remove the Bill as well. To delete either, open the appropriate transaction and at the bottom select More – Delete.

Resolution for Issue 'Can I undo a paid bill?' available: Yes (Solved).
Source: Intuit Community forum.

Can I undo a paid bill?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for Payment
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Error Recovery for Payment [Canada]
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