The return authorization code, or RMA number, is issued by the merchant after the buyer agrees to return the product when the buyer submits a return request. The system is primarily used by overseas warehouses to identify return packages from various OMS customers that do not have a logistics order number.

Because the outer packaging of the Amazon return package is the same, it is impossible to tell which customer returned the goods; therefore, the RMA number can be filled in on the Amazon invoice using the recipient plus return batch number, for example: Jason-01.