QB Issue Resolution:

If you go to the cog in the top right>account and settings>advanced>accounting>close the books

There is likely a date in there,it may have been put in by the migration team,you can remove it by taking the tick out of the box in that sections and then saving it

Resolution for Issue 'Saving an invoice I get a box saying: Double check transaction date. Says date is on or before company closing date? I select to carry on but is this OK?' available: Yes (Solved).
Source: Intuit Community forum.

Saving an invoice I get a box saying: Double check transaction date. Says date is on or before company closing date? I select to carry on but is this OK?: 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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