Your quotes and invoices each have their own numbering system, which you may have already configured. Here's an example:
What happens when I convert quotes<>invoices?
Converting a quote to an invoice will cause a change in the ID number, since quotes are treated differently from invoices. But what if you need to convert an invoice BACK into a quote?
The good news is that you can do this, and the original quote number will be retained without any issues to the existing quote or future ones. So for instance, if Quote #400 is accepted and converted to an invoice, and then back into a quote later, it will once again take on the title of Quote #400.
What happens if I delete a quote or invoice entirely?
If you delete a quote/invoice, what happens to the numbering depends on when you deleted the quote/invoice. If you delete the newest quote/invoice, then the following one that you create will take on that number, since it has become available. For example, if you delete Invoice #3 and then create an entirely new invoice afterwards, that new one will be called Invoice #3.
If you delete a quote/invoice that is not the latest one, then its number will be removed entirely, and will not be replaced. See below for a visual of both situations:
