The BAPI function module BAPI_ISUPARTNER_CHANGE allows you to modify the BP Type (field name BPKIND). You will find documentation in the BAPI Explorer.
I can tell you that the German colleagues in SAP consulting offer a solution to change the BP type (similar to a CDP offering). I am unaware of the costs for this solution. You can contact (rainer.lork@sap.com) if you wish to pursue the solution.
You should only submit an answer when you are proposing a solution to the poster's problem. If you want the poster to clarify the question or provide more information, please leave a comment instead, requesting additional details. When answering, please include specifics, such as step-by-step instructions, context for the solution, and links to useful resources. Also, please make sure that you answer complies with our Rules of Engagement.
Add a comment