Supplier &1 and supplying plant &2 incompatible

What causes this issue?

You have entered supplier &V1& and supplying plant &V2& in the source
list. However, a different supplying plant has been assigned to supplier
&V1& in the master record.

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?

Enter either the supplier or the desired supplying plant.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.