Internal document numbers determine document series, and overwriting them is not standard practice. You'll encounter them in the Sales, Purchases, Money, and Accounting modules.
⚠️ If you need different numbering, do not modify an already recorded and used document series — always create a new one. Making changes to a series that's already in use leads to inconsistent document numbering.
Enabling manual overwriting
If manually editing internal numbers is necessary, first enable the feature:
Go to the menu Company → Settings.
Switch to the Other tab.
Check the Allow manual overwriting of internal document numbers option.
The internal number can then be overwritten manually on a document, one document at a time.