Android : Android App sends Data only Using Wifi

I have a question to ask, I created an Android App where i am sending Data to Xampp server (Using HttpClient) and storing it in a Database. My App does,not send Data using Mobile Network , even tried with 4G but the Application stops but works with wifi. I just wanted to know why does my App only works with Wifi and if somebody know how to make it work using Mobile network eg the way Viber works

Thanks .