For sales org. &1, distribution channel &2 is not allowed

What causes this issue?

The error analysis of the defective record showed that an assignment of
the distribution channel to a sales organization was not permitted.

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?

If you no longer need the assignment, please delete the line.
Otherwise, maintain the assignment of distribution channels to sales
organizations and then call the assignment again.

Error message extract from SAP system. Copyright SAP SE.