Need help with port forwarding on a PPPoE connection.

I have a PPPoE connection and a TP-Link router, I wanted to do port forwarding and in my router settings there is an option called "NAT Forwarding" where in i have entered my PC's IP Address which is connected to my router using ethernet cable, in external ip i have 3737 and in internal also i have 3737. So to test this i ran a python http.server module and tried to connect from my mobile using mobile data but it doesn't work it says connection timed out. But when i connect from my mobile using my WiFi it works.

Pleae Help.