This article explains the difference between the serial RJ45 port on EloPOS and RJ50 on EloPOS Pack and if the cables are interchangeable

EloPOS Pack features an RJ50 serial connection, while EloPOS features an RJ45 serial connection. Each of these products includes a RJ to DB-9 converter cable. While RJ50 and RJ45 are the same physical size, they are not interchangeable. RJ50 contains ten pins, while RJ45 only contains 8 pins. For more information on the specific pin-outs of your product, see these additional knowledge base article. 

EloPOS DB9 to RJ45 Cable Pinout
EloPOS Pack RJ50 Pin-Out