I had the same issue earlier.

I raised a support ticket along with diagnostics. The initial reply suggested changing the wi-fi channel, but I don’t think this had anything to do with the problem as other sources played without problems. Changing channels made no difference so I moved my router back to the original wi-fi channel (1).

I pointed out to support that others on the community forum were reporting exactly the same error so in my opinion it was an upstream issue.

Sonos Radio started working again about a couple of hours ago. I am still awaiting a response from the support team as to what the root cause was. 

I have the identical problem. Have been using Sonos Radio for some years and suddenly it required re-authorization. Unable to even enter a username or password, just keep getting error, problem authorizing your account.

Wonder if there’s something going on due to the legal issues TuneIn is having. I’m pretty sure Sonos uses some TuneIn streams to feed Sonos radio. Perhaps it was a poor attempt to disassociate. Pure conjecture on my part.