Find your IP by using a service such as https://www.whatismyip.com/
In order to open up your port (3415), you need to configure your router appropriately to forward traffic from the router to the machine where your wallet listener is deployed (usually by accessing your router via a local IP such as http://192.168.0.1, may be different in your environment).
To find the local IP of your wallet’s host, do ifconfig in the host, figure out the correct interface from where you get internet access (wifi is usually something like wlp3s0, may be different in your environment), and use the IP of that interface in the port forwarding rule in the router.
Then, update api_listen_interface to 0.0.0.0 in ~/.grin/main/grin-wallet.toml and run grin wallet listen.
At that point you should be able to verify that your port is open at https://www.yougetsignal.com/tools/open-ports/ and all set to receive grin via http.
Sincerely, good luck!