Partner function &1 (business partner &2) not permitted

What causes this issue?

&V4&:
Partner function "&V1&" (business partner &V2&) is not permitted in
partner determination procedure "&V3&".

System Response

You have assigned a partner function (&V1&) to marketing project &V4&.
This partner function is not permitted in the selected partner
determination procedure.
In the partner determination procedure you define which partner
functions may be used. Other partner functions cannot be used.
Depending on the object class, the partner determination procedure is
either assigned using the type or directly in Customizing. The
assignment of partner determination procedures to types is also made in
Customizing.

How to fix this error?

You have three options:
1. Change or delete the partner function (&V1&) that is not permitted
for business partner &V2&.
2. Assign another partner determination procedure to the marketing
project (either by selecting another type or by making another
definition in Customizing).
3. Include the partner function "&V1&" in the definition of the partner
determination procedure "&V3&" in Customizing.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.