Append structures can only be created from the menu

What causes this issue?

You tried to create an append structure by entering APPEND in the field
list. In contrast to includes, this is not possible for append
structures.

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?

Create the append structure by selecting the function <LS>Goto ->
Append structures</>.

Error message extract from SAP system. Copyright SAP SE.