User-defined Partner Function Derivation during Sales Order Creation

Dear Expert,

We have some user-define partner function like "Sales Support Team" and derivation rule is created to derived the values in COPA.

Derivation step used - Table lookup

Source

VBPA-VBELN CO-PA-VBELN

VBPA-POSNR CO-PA-KDPOS

VBPA-PARVW Global-USERTEMP1 (Consant-ZR)

Target

VBPA-KUNNR CO-PA-WW250

Issue is that when we are creating Sales order during the creation derivation not taking place.

as during the sale order creation in VBPA table sale order not exist without saving order sales order not update in VBPA.

so trying to some user exit but not able to proceed further how to define same .

request expert put your expert view.

Thanks

Akesh Agrawal