Hello!
I'm not sure concerning the relationships between APP and FSCM, but I think that there should be some link between FSCM and EBS. Go to transaction OT83 ("Make Global Settings for EBS") and choose tab "Assign External Transaction Types to Posting Rules".
Choose the external transaction relevant to your customers and check the entry in the column "Planning Type, Transaction". I think some of them (e.g. General planning) might be helpful.
Hope this will help.
Best Regards,
The Wirtschaftsmann