RBR40 router not connecting to Xfinity

[Griffin_nova]

Brand new here.  I purchased an RBR40 router with two satellites from BestBuy.  I have Xfinity cable internet service and have been using an Arris 8200 Surfboard modem for over three years.  My current wi-fi network is a first generation Google mesh set-up.  I wanted to upgrade and chose the Orbi.  I followed the setup steps in the mobile app but the router will not connect to the internet even though the modem indicates an internet connection and transmission from the port.  Now, I can reconnect the Google setup and it works fine.  I'm at a loss.  Is this the router? the modem? Xfinity? or what?

[plemans]

Which arris is it? The SB8200?

If so try this. 

power off the sb8200 and the orbi and disconnect all devices/wires from both. even coax. 

Then connect coax back up to modem and power it on. give it several minutes to fully boot. 

The connect port 1 on sb8200 to wan port on orbi and boot up orbi. give it several minutes. 

Try setup. Make sure to leave port 2 on SB8200 with nothing plugged in.