Solved Mobile app refuses to register on T-Mobile network.

[Ty23465]

We are having issues with the mobile app not working at all on any phone that is using the T-Mobile network. We have one user who has Google Fi on IOS and a user with Mint mobile on Android and both quit registering. The first we noticed this was yesterday but it may have been longer. Bother devices worked previously and when you try to reinstall the app it says the QR code is invalid when using mobile data. As soon as you turn on a VPN or connect to a wifi network everything works fine. We tested a device on Visible(Verizon), and it worked fine.
We are on 3CX SMB and everything had been working fine for a few months.

 

[Alphabetic]

Are you able to get an app that will allow you to ping your FQDN when on the T mobile network? Or try get to the web app from browser.

 

[Ty23465]

I tried to access it from the browser and it did not connect. I setup private DNS with google.dns and it worked. It appears that whatever DNS server T-Mobile is using is not pointed to the correct IP address. Not sure if this is a 3cx issue or a T-Mobile issue but it is frustrating

 

[Alphabetic]

Check if the fqdn is resolving to an ipv6 address and if so check your 3CX has an ipv6 address. Try pinging google too to see if it’s ipv6

 

[Ty23465]

It appears to be resolving to both an IPV4 and an IPV6 when using googles dns. When on T-Mobile it does not resolve to an ipv4 or ipv6. Under the admin dashboard of 3cx it shows both an IPV4 and an IPV6.

 

[Ty23465]

Update! I contacted T-Mobile and they claimed there was tower upgrades in the area. Two days later and everything is working as normal.