Are you launching the Arris app from your phone? Does the phone access the internet properly when running other applications? Basically trying to understand whether you have a valid WiFi connection to your SG7600AC2 from the device.

Yes, I am trying to connect to the app from my phone and the phone is connected to the Wi-Fi but I am getting a message in the app that the wireless gateway is not connected.

I deleted the app from my phone and reloaded it but I am still getting the same message that my device/phone Wi-Fi is connected but my phone shows it is connected.

Try performing hard reset on the router then uninstall and reinstall app then start the setup if you get the same error you can try toggling WIFI on the device that will help you in configuring the application successfully.