@LouiseG  RE: Having different invoice numbers in QuickBooks Online (QBO) ensures accurate transaction tracking, avoids duplicates, and maintains organized records.

No, it doesn't. It doesn't do any of those things. Instead it's just an overly restrictive annoyance.

There are good reasons why QuickBooks Desktop lets you do this. It puts up a warning by default, which you can turn off, but it lets you do it.