The partner funct. entered is not defined in determination procedure &

What causes this issue?

The <GL:partner_function>partner function</> that you selected is not
defined in the <GL:partner_determination_procedure>partner determination
procedure</> assigned to the notification type.

System Response

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

How to fix this error?

Check your entry. Change the partner determination procedure assigned to
the notification type, or expand the existing partner determination
procedure.

Error message extract from SAP system. Copyright SAP SE.