Prefix for temporary keys does not exist

What causes this issue?

No prefix was defined for temporary keys. However, a prefix is required
for entity types with internal key assignment.

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?

Perform the Customizing activity <DS:SIMG.MDG_V_USMD016>Define Prefixes
for Internal Key Assignment</>.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.