ckgw
I've recently had this issue when launching the apple tv on roku, it just spins forever. I tried everything including network connection resets, reboots, factory reset on the roku, different network connections, etc. For me, it worked in one location but not at a second location I watched at. I was able to fix it by updating to a different dns setting on my router (it usually defaults to the ISP default, which may not be great)
This fixed it for me. Keep in mind, if you can get a prompt to login to apple tv this will not help. But, if you open the Apple Tv app on roku and it just spins forever (may error out) it is highly likely the dns is not resolving correctly to Apple IP's.... good luck!
Go into your wifi router settings and update to google's dns server.
Primary DNS 8.8.8.8
Secondary DNS 8.8.1.1.
Save the changes, a router reboot maybe needed.