There is a difference between Samsung Pay and LoopPay. Your phone supports LoopPay just fine because to use LoopPay you need to have a LoopPay card in order to pay with your phone which is a separate dongle that can be acquired from the LoopPay website and the LoopPay app. Samsung Pay uses the technology that was built into the LoopPay card case in order to allow you to pay with your phone. The LoopPay technology has only been built into the most recent phones: the Galaxy S6, S6 Edge, Note 5, and S6 Edge+. Your phone simply does not have the hardware required to use MST in Samsung Pay. If you only want to use the NFC function of Samsung Pay then you might as well just use Android Pay it is the same thing.