Organization unit & does not exist

What causes this issue?

You have attempted to run the function using an invalid organizational
object. Specifically, the R/3 Repository domain on which the
organizational object is based is not available.

System Response

The system cannot execute the function.

How to fix this error?

SAP: Use suitable organizational objects or domains.
Customer: Check the ABAP Dictionary to see if the domain exists. Use
Transaction ECOP to see a list of permitted domains.

Error message extract from SAP system. Copyright SAP SE.