Unable to add second hub

Brand new c8 hub. I’m trying to add a second hub to my existing network. I plugged in Ethernet, plugged in the power. The hub goes from blue light to green… then the light blinks between green and red. It’s connected to my lan as I can see the hub on my lan, and it’s passing data.

I’m stuck, though I’m also an idiot.

Um, no you are not. Try resetting the hub's network settings. It's an odd behavior. Have you tried to connect it via Wi-Fi at first?

I’m not even sure how to do that…

Follow these instructions: Network Setup | Hubitat Documentation

I did this several times and still the same thing. I'm wondering if the ethernet cord that came with the HE is bad. I'll need to try changing that out the next time I'm there.