Hello Richard,
You have to create another logical name T90CLNT090, client : 090 on ECC side.
1. Create new log.name T90CLNT090
2. Assign new Log.name to client 090
3.Specify APO release - normally this step is already done
4. Set up new RFC Destination - have to point to SCM logical name
5. Assign RFC Destination to Diff.Applic..Case - (RL,RQ)
6.Set target system and Queue Type
If all these steps are done on ECC side then you can point the RFC Destination from APO to ECC to newly ECC logical name T90CLNT090. In the tab Technical settings you can work with IP Address or Hostname. Try to work with Hostname. In this case the Hostname will be identical with Target Host.
Thanks, Marius