There is no partner with a customer account for loan &1

What causes this issue?

You have attempted to assign a partner to a flow record. This is not
possible, since the underlying loan is not managed on the basis of
customer accounts.

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.