If this is an ongoing credit for beverage credits such as a keg or bottle deposits, you'll need to create an item in ingredients called Keg deposits and returns. Your vendor should assign an item code to that credit.
When you receive a credit on your invoice reciProfity will match the item code and read the number of products returned and display the credit amount. This credit amount will be associated with your current On Hand.
Your On Hand will display both the original deposit charge and once the keg/bottles are returned you'll see the deposit refunded: