@bd103 @Rin3d
Generally, like this: Identift any way to reach the device from the outside. With CGNAT the main thing to test is ipv6. I like
https://github.com/svenstaro/miniserve as a simple tool to run a small HTTP server. Run it in an empty directory and it'll start serving it over HTTP, giving you a list of possible addresses. I'm recommending miniserve because it shows a list of adresses on any system. If it doesn't show any address with 4-character blocks separated by colons, ipv6 isn't working and you probably need to enable it in your router or device settings. Look up the first block of 4 characters to see which of the addresses miniserve lists is a global address. Before this is accessible globally you'll likely need to open up the port in your routers firewall settings - ideally just the port miniserve uses. Then, try opening that IP on your phone using the mobile network (wifi off) - if it works, great! If it doesn't, troubleshooting might involve checking if miniserve is accessible through local network, checking ipv6 settings of the device, trying different ports, different router firewall settings, and worst case reaching out to the ISP to ask if they've blocked inbound ipv6 (most don't), or specific ports, and if they do, whether they can unblock it.
If it works, you probably still don't have a fixed ipv6 prefix, so you'll want to run some Dynamic DNS (DynDNS, DDNS) tool which automatically updates DNS records to always point at your devices global ipv6. Theres services offering a domain for this for free using a subdomain, or you can get a cheap domain for 6-9$/year. I like Porkbun as a registrar (= company that sells domains). Note: this is not redirecting or hosting anything, DNS is like the address book of the internet. DynDNS is just updating the address automatically, so if it changes, you don't have to do it manually.
