Android gamepad not working

i am using ue4 4.19.2 but when i play game in my mobile phone the gamepad is not working .

i map the input key with raw input generic usb but this not work in mobile.

Analog sticks and d pads are working fine. Then i add printstring with all other keys. So when i press any button of gamepad this shows gamepad face button bottom. With left shoulder trigger or others keys show the same msg