Change request type &1: Main entity type &2 does not exist

What causes this issue?

You have specified <DS:DE.USMD_ENTITY_MAIN>main entity type</> &V2& for
change request type &V1&. However, entity type &V2& is not (yet) one of
the entity types that can be processed with change request type &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?

In the <LS>Entity Types </>subdialog, add entity type &V2& to the list
of entity types that can be processed with change request type &V1&.
Alternatively, specify a different main entity type for change request
type &V1&.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.