QB Issue Resolution:

bring the transaction up on screen, use the more menu at the bottom and select delete

Resolution for Issue 'How do I delete a transaction that has been posted and saved?' available: Yes (Solved).
Source: Intuit Community forum.

How do I delete a transaction that has been posted and saved?: 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.

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