Table has a long field. It is not possible to create an append structure.

What causes this issue?

The edited table has a long field, that is, a field of type VARC, LRAW
or LCHR with a length greater than 255. Such fields must be the very
last table field. Therefore, no APPEND structure can be added to the
table.

System Response

Creation of an APPEND structure was rejected.

How to fix this error?

You cannot create an APPEND structure for this table unless you first
delete the long field and then activate or adjust the table in the
database. Please note that data losses may occur.

Error message extract from SAP system. Copyright SAP SE.