I just renewed a piaware install I had on an old RPi. It was running some ancient version of Debian and piaware, so I just started from scratch using the latest Raspbian Buster release and the 3.8.1 installer flow.
We’ve had recent network problems (see https://twitter.com/FlightAwareOps for updates) and this is probably collateral damage from that. I’ll check with ops about getting it fixed.
In the meantime, you may be able to work around it by going directly to https://flightaware.com/adsb/piaware/claim/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx (insert your own feeder UUID - piaware-status will tell you what that is).
(This is also where the claim-this-feeder link on a piaware sdcard image’s top-level status page will take you)
This should be working again now (or at least in a little while, after DNS propagates), please let us know if you run into further problems; sorry for the hassle.