Target server group & is empty or does not contain a suitable server

What causes this issue?

The named server group is not suitable for this request.
Either the target server group is empty (see SM61) or there are no
resources for background processing in the target server group (Job
class, and so on).

System Response

The system does not accept your entry.

How to fix this error?

Choose a different target server group or maintain the target server
group using SM61 (Maintaining Background Control Objects)

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.