Smartphone external IP problem

I’m trying to connect my game to the server and It’s working properly in the same network and unlocking the port forwarding in my router. So I can connect using my smartphone 3G/4G to my external IP from my router or both local.

Working: Same Network (Android-Client) --> Same Network (Desktop-Server).
Working: 3G/4G (Android-Client) --> My external IP from my router (Desktop-Server).

Working: Same Network (Android-Server) --> Same Network (Desktop-Client).
Not Working: 3G/4G (Android-Server) --> Same Network (Desktop-Client).

This is weird because I can’t ping to my 3G/4G external IP using ping command, but I can connect to my desktop server from 3G/4G android client.

I’m getting the external IP of Android device provider here (accessing with android browser): https://www.whatismyip.com/ but the ping to this IP don’t work.

Maybe 3G/4G internet protocol need some additional information in the address?? ???