Domain & is not key domain of value table &

What causes this issue?

A domain can have a value table assigned to it which has a key field
with this domain. This assignment forms the basis for the definition of
foreign key relationships for table fields with this domain.
The value table specified for the domain does not have a key field with
this domain.

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?

Specify a table as value table which has a key field with this domain
or modify the specified table so that it meets this requirement.

Error message extract from SAP system. Copyright SAP SE.