frontaccounting - open to bidding

I am in distribution business. I sell my product to my customers , End of the month I have to pay them shelf rent / stocking fee, I am getting a hard time to figure how to record this payment. I tried posting a payment under bank and GL , the money transfers fine from my bank account to the customer but then it the customer transaction it shows as an amount he ( customer ) owes me. which he doesn't owe as it is an expense for me for sales. what to do any help please