Brand new account. No router receives internet from modem.

Hello. New Xfinity customer here. I purchased a brand new Motorola MB8611 to use with my newer TP-Link Deco mesh system. I also have a TP-Link Archer AX50 as backup. 

My previous setup was CenturyLink Modem > AX50 > Deco, where the Deco was still in router mode and not access point. Everything worked very well. 

In our new home, though, I just need one network, but need it to reach further. So I want to do just Modem > Router/Deco. All of the equipment is mine, not owned by Xfinity. 

I set up the modem using the Xfinity app and that went off without a hitch. However, when I tried to plug in the Deco, it gave me a solid red light, meaning there was some sort of issue. Long story short, I finally got it factory reset and set it up as a new network. It shows that it is not receiving internet connection. 

So I unplugged that from both power and Ethernet, and tried to setup my AX50. I factory reset it before plugging in the Ethernet. Set it up as new. No connection to internet. 

The modem is showing all good signs - all blue icons on the front, and Xfinity app shows it’s good. I’ve restarted it several different ways. 

What’s going on here? Do I need to manually apply any specific settings in the routers’ dashboards to get Xfinity to work?