No transformation rule assigned for domain &1 (&2)

What causes this issue?

No transformation rule assigned for data element &V1& (sequence number
of RAS entry &V2&)

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?

Go to the tab 'Rule Assignment' of the embedded specification and check
the settings done for domains, data elements, and table fields. There
should be one assignment without an associated transformation rule.
Correct this entry and re-execute this activity again.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.