No configuration for proxy class "&1" and logical port "&2"

What causes this issue?

A program has tried to instantiate a proxy with a Logical Port.
The SOAP Processor could not find this Logical Port.

System Response

Since the SOAP processor could not find the requested Logical Port, it
was not possible to process the Web Service call.

How to fix this error?

Please maintain this missing Logical Port as described in the
Implementation Guide of the consumer application.

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.