Solution : https://service.sap.com/sap/support/notes/376445 (SAP Service marketplace login required)
Key words : 
additional key words tvak-vstrm, sales document type, function modules sched_catalogue_build, scheduling function existing, tvak-trtrm, transportation scheduling, complete scheduling, apo scheduling, apo shipping, switches correctly
Related Notes : 
       
| 382746 | Collective note: Delivery+transportation scheduling with APO | 
| 376442 | Scheduling: R/3 flag TVAK-VSTRM/TRTRM | 
| 328972 | APO integration of scheduling | 
| 322509 | APO integration of scheduling "Exit inserted" |