Destination &: The first key field of table & is not MANDT

What causes this issue?

The destination &V1& of type "ABAP/4 table" has been assigned to the
selected process message via the message category. However, for one of
the following reasons, process messages cannot be transferred to the
destination table &V2&:
The MANDT field is not the first key field of the table.
The domain assigned to the MANDT field does not define the same data
type as the MANDT domain.
The domain assigned to the MANDT field does not define the same field
length as the MANDT domain.
The process message has not been sent to the destination &V1&.

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?

RESET N1
Check the definition of the table &V2& in the ABAP/4 Dictionary and
correct it according to the requirements listed above.
INCLUDE 'NA_EMPF_SEND' OBJECT DOKU ID TX LANGUAGE E
Otherwise, maintain the table entry manually, if necessary.

Error message extract from SAP system. Copyright SAP SE.