App (Android) can not connect to the server - java

I have a problem with my android application. In Android Studio, everything looks normal since no error appears. The application is supposed to connect to the web server for data recovery. But every time I test the app on my android device or on an emulator, I still have the same message: "Appname can not connect to the server"
So, since I do not see any error on Android studio, I do not know where to look. I tried with the coordinates of two different servers, but still the same message. I have concluded that the problem is not at the level of the connection to the server, but in my code, but where?
If anyone has any suggestion, I'm a taker. If you need to see any file, let me know.

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