Unkown error calling function module &1; net calculation canceled

What causes this issue?

Net calculation called a function module of another area (such as SAP
Business Partner, for example) to execute some checks or services. The
function module has returned an unknown exception.

System Response

Net calculation processing cannot be executed.

How to fix this error?

Contact your system administrator.

Procedure for System Administrators

The referenced function module is &V1&. If you cannot determine the
cause of the problem, contact SAP with the details of this error.

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.