The terminal will provide a link. Follow that link on your mobile browser. Enter your PUBLIC IP address.
With so many ISP assign dynamic IP address to their customer, it doesn't seem to be practical. Entering new IP address when you reboot the modem or ISP assign new IP address after some time is rather cumbersome.
I have replaced localtunnel with tunnelmole, so now entering the public IP is no longer required. That was some major friction that I’m glad is gone. I may be able to edit the conf file automatically too, but it might be best to leave that to the user.