Before setting up the app, Have the web-based interface (GUI) set up? If you do, follow the steps for a device that is already set up with the web-based portal on the app.
If you haven't set up the GUI before, we need to verify if the GUI is misconfigured. The Surfboard Central app pairs with the gateway and syncs with the web-based interface (GUI) as well.
First, connect your phone to the Wi-Fi and check if the internet connection is working. Then, connect a device like a laptop or phone to the network, open a web browser, and type http://192.168.0.1 in the address bar. You should see the ARRIS interface page (GUI). If the page asks you to create a password, the modem is not misconfigured. In this case, restart your mobile phone and start the setup on the app again.
If the GUI page asks for an email address and password for login, it indicates the page is misconfigured. We recommend performing a factory reset. Hold down the reset button for at least 20 seconds and then release it to reset the gateway. Wait for it to boot up.
After confirming everything is working, start the setup process on the app again. For your reference, please find the link below for the steps to set up the app.
http://arris.force.com/consumers/articles/knowledge/SURFboard-Central-Wi-Fi-Cable-Modem-Setup