Cash receipt routed to a specific account

Hello,

I´m trying to allocate a cash receipt with a discount to a specific account ( BU-Obj-Subsidiary; for instance, discounts taken by EU customers go to subsidiary 100). For that purpose, I have added to the customer address book cateogry code 09 (100) the same subisidary code to have a connection between the account and customer.

I have also set up reason code for the discount (00/DE) and attached that with RKD AAI (RKDXX). AAI is set up with the subsidiary 100. When I enter the cash receipt it still finds its way to BU-Obj and not BU-Obj-Subsidiary. I assume I´m missing a connection between the customer and AAI? Could someone please suggest how could I get this set-up to work?