Recently we get some clients report ,they can not connect reachfar App and web system www.gps123.org while they are on mobile networks, but will only function when connected to wifi.

If wifi can be conencted to App and web system,that means the App and web system runs well.it should be phone's cellular networks DNS setting issue.

Please try to check as following steps:

Android Phone:

Please check Are you running a VPN on your phone by any chance? If so, turning that off should solve the issue.

Otherwise, I would recommend you try clearing your DNS settings on your phone. You can do this by performing a hard reset. Remove the battery for about a minute and then restart.

If you do not have a removable battery, then try clearing your browser history from each of your browser apps. For Chrome you can visit chrome://net-internals and choose DNS for clearing options. You can also flush the sockets under the socket menu.

iOS Phone:

Apple has not included the ability to change the DNS details for cellular connections in iOS. By default, users are stuck connecting to whatever DNS server is set up with their carrier(SIM card provider.).

It is possible to make changes to the cellular DNS, but only through the use of third-party applications.

One option is DNS Override, a tool for changing the DNS details for Wi-Fi connections,. Once unlocked with an in-app purchase, the app effectively creates a dummy Virtual Private Networking (VPN) profile that isn't actively used, but does allow for the app to set the DNS server, including for cellular networks.

Please have a try ,if still have problem please connect us feel freely.

ReachFar Tech offer the best dog tracker ,cat tracker,personal tracker,car tracker and gps service for you.

More detail please refer following web

https://appleinsider.com/articles/18/04/22/how-to-change-the-dns-server-used-by-your-iphone-and-ipad

https://www.androidpolice.com/2019/12/14/make-android-use-dns-server-choice/