Hi wisdom82
Welcome to the Community Forum. It is possible for 2 invoices to have the same invoice number, however you can tell the software to show a warning to prevent confusion.
There are 2 preferences you might want to turn on:
1. To prevent duplicate invoice numbers being used:
Setup > Preferences > Sales> Warn for Duplicate...Numbers on Recorded Sales
Setup > Preferences > Purchases > Warn for Duplicate...Numbers on Recorded Purchases
2. To keep the same invoice number when converting a quote or order to an invoice:
Setup > Preferences > Sales> Retain Original Invoice Number when Quotes Change to Orders or Invoices.
Setup > Preferences > Purchases > Retain Original PO Number when Quotes Change to Orders or Bills.
Please let me know if you have any further questions.
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