Trouble using "Activate now" option.

I'm trying to use Activate now option in the Xfinity app. However, right after selecting "Your own modem", it throws the error "Sorry, we're having some trouble. Please chat with an agent for help with your activation". I was able to use this option earlier to activate my new modem. However, right after activation, it got restarted and never came back online. I have been having this issue since then. The xfinity technician suggested that the issue is with my new modem and so he reactivated my old modem. But the problem is that I'm not able to use the app to activate any other modem. Please help me resolve this issue. I suspect that the issue is at the backend.