QB Issue Resolution:

Instead of editing a previously saved invoice, you need to create a new invoice with the number you want to use and save it.  Then, the next invoice created will continue numbering from there.

Resolution for Issue 'How to get invoice numbering to start at the number I choose and number automatically from there? (I have already selected the custom transaction number)' available: Yes (Solved).
Source: Intuit Community forum.

How to get invoice numbering to start at the number I choose and number automatically from there? (I have already selected the custom transaction number): 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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