If your app displays a network error message, try the following:
1. Turn Wi-Fi OFF in Settings > Wi-Fi > Off
2. Turn Airplane Mode OFF in Settings > Airplane Mode > Off
3. Turn Cellular Data ON in Settings App > Wireless & Networks (header) > More... > Mobile Networks > Data Enabled.
If these steps don't solve the issue, try restarting your phone by pressing and holding the power button and selecting Power Off or Restart.