ABAP dictionary data type &1 is not supported.

What causes this issue?

Most ABAP dictionary data types are supported by the app <ZK>Custom
Fields and Logic</>.
<ZH>Not supported </>are obsolete data types like PREC, binary/character
large objects (BLOBs and CLOBs) like STRING, technical data types like
CLNT, and data types which require a preceding field for length
specification like LCHR.

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?

You may want to check whether the data type of your current database
field can be changed to a supported data type without data loss. Please
refer to the ABAP Dictionary documentation in order to check whether
this requirement can be fulfilled.
Otherwise, your database field cannot be enabled for use in app
<ZK>Custom Fields and Logic</>.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.