Function module & does not exist

What causes this issue?

Function module &v1&, which should assume reponsibility for further
IDoc processing, has been stored for port &v2&.
However, this function module does not exist and the IDoc could not be
processed further.

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?

Please change the port definition for port &v2& or create function
module &v1&.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.