AUR broken? You're not alone.
ArchLinux updated the AUR API and the old URLs don't work anymore. This is a bit awkward, as your AUR helper now can't get access it and can't even update itself any longer. This means you will have to manually intervene to resolve this situation 😕
If you're using yay, here's a quick fix that patches your old binary:
sudo sed -i 's:rpc.php:rpc////:g' /usr/bin/yay