Sales Order availibility check not triggering GATP in APO

Hi Gurus,

We intend to use GATP in APO. When Sales Person enters any SO and presses for availibility check, it should trigger availibility check in APO. in APO we intend to use RBA with Location substituation rule.

Following are the settings done:-

1) Integration Model for Plant.material and SO are created and activated

2 Created Integration Model for ATP check and ATP customizing

3) Created Check Instruction in APO for check Mode : 050 and Business event : A

4) Created Check Control with ATP Group : 2 and Business Event : A

5) Created all necessary configuration for Location substituation under RBA configuration.

Currently when we create a sales order and selects the item for availibility check , it does a local ATP check in ECC , but it does not trigger GATP in APO.

Am i missing any configuration or master data setting?? Any help will be appreciated.

thanks,

Jaideep