Arris iPhone App does not work

Could you please help us with your product’s model number?

ARRIS - SURFboard S33 32 x 8 DOCSIS 3.1

Syncing what 2? 

the S33 is a modem only device. You don’t need the app for anything. You’d just need to have it activated by your isp. 

As ​@plemans  mentioned, the S33 is just a cable modem, and activation must be completed through your service provider.

For Wi-Fi functionality, please note that you will need to have a separate router in addition to the S33 modem. The S33 is designed as a cable modem and does not include built-in Wi-Fi capabilities.

If you would like to add the S33 to your account, you can simply remove your previous SURFboard modem from the app and then add the new one. If your internet service provider offers a self-activation method, you can also activate the modem using the SURFboard Central app. In addition to that, the app allows you to register for warranty support.

Please note that it is not possible to have both modems on the same account at the same time. You’ll need to remove the old modem and add the new one, or you can sign out of your current account and register the new modem with a different email address.