Hello there, Simon_Q.
Let me help and provide clarifications on what will happen when you use the same transaction number in QuickBooks Online (QBO).
When you enable the "Warn if duplicate journal number is used" feature, it prevents the online program from duplicating the number for your journal entry. Thus, it won't cause any clash in your transactions. Thus, it won't cause any clash in your transactions.
If you did not activate the function, you will be able to use the same journal number for the entry (duplicates). I've provided some links below that will help you enter a journal entry and swap the debits and credits on a transaction:
The following link also has a list of topics that cover managing your cash flow, processing payroll, handling banking information, and other accounting-related tasks: Self-help articles.
If you have any clarifications about transaction numbers or other QuickBooks concerns, tap the Reply button and enter them in the field box. I'll get back to help you the best that I can.
