Partner Determination for STO

Hi All,

I have a small probelm here. Whenever I try to create a STO, the partner (DP) is not determined automatically. This happens only with PO type UB.

The configuration looks ok thou.

I have the partner schema 0003 assigned to Partner fucntion DP. And the partner schema is assigned to PO document type UB.

Am I missing anything? Can this be done....I read somewhere that this needs to be done in a user exit...

Thanks and Have a nice day.