Check table & is also foreign key table

What causes this issue?

The table itself was specified as check table. Only those values which
already exist in the table are therefore possible. For this reason no
values could be entered in the table.

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?

Delete the foreign key to the field or remove the flag for the key
field.

Error message extract from SAP system. Copyright SAP SE.