Issues with recognizing fiber optic signal

Thank you for the info!

The ISP provided me with these two devices: A Calix Gigapoint 803g ONT (pictured) and a Centurylink C4000xg Wifi 6 modem/router combo. However, I didn’t think you needed a modem with Fiber. That’s what I don’t understand. I thought the ONT was the “modem” that translates optical signals to digital in a Fiber network.

I am trying to plug my GLiNet routers directly into the black ONT INSTEAD of using the CenturyLink router/modem. But I don’t get a signal. The CenturyLink router/modem works just fine though. So I’m wondering if the modem part DOES have something to do with it…