Use a data element with domain to specify the data type of the field.

What causes this issue?

To use your database field in the app <ZK>Custom Fields and Logic</>,
the data type of the field must be specified using a data element with
domain.

System Response

The field labels specified in the data element will appear as field
labels of your field, for example, in apps, reports<(>,<)> or print
forms.
The domain will be used by the app <ZK>Custom Fields and Logic</> as
reusable data type specification.

How to fix this error?

Choose either an existing data element with domain<(>,<)> or create a
new domain and data element in transaction SE11. The type specification
of the domain must be compatible with the current built-in type
specification of your database field.
Start transaction SE11 and open the structure which contains your
database field.
Switch the data type specification for your field from <ZK>Built-In Type
</> to <ZK>Component Type</>.
Enter the data element name as <ZK>Component Type </>and activate the
changes.

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.