Radarr can’t authenticate with trakt.tv anymore. When I accept the authentication I just get a new page saying “Received oauth token was invalid.”
Help plox.
The API is not back up. I would try again later next week and keep an eye on Trakt twitter.
Aha, okey. Thought everything was up again, then I will try again next week! 
Please take a look at https://status.trakt.tv and see that all API endpoints are red.