ID Prefixes are predefined on Document Type level.
Each Document Type needs to have at least one ID prefix. Multiple ID prefixes per one Document Type are possible as well.
You can create more ID prefixes by clicking on the + button on the Document Type Form page:
You are able to remove an ID prefix by clicking on the - button on the Document Type Form page but only if there is not a single Document created with this ID prefix:
Relevant for: Administrators / Managers.
Please note: An ID Prefix cannot be changed anymore once a Document has been created with this specific ID prefix.