I’m sorry that you are getting this error! This is actually related as we are having trouble connecting via the fly api. For this reason, I have merged your post here so that you will be notified once this is fixed.
Have you ever looked into alternatives to fly.io that could help you set up your reverse proxy domains thing? Or make your own software to do so, like @ihack2712’s ‘Glix’? Fly.io have said you are using deprecated features of their service, so it might be time for a change.
It seems to me that you are kinda placing all the stress on fly.io when they don’t get much benefit from it. Have you ever thought about the possibility that fly.io may not be the best partner and may not fix everything for you. Mind you, I don’t know how the partnership works
its technically is possible with their current system, they might have to tweak it a bit but they already use reverse proxies from the *.glitch.me domain to port 3000 on (what im guessing is) a docker container. it would break all custom domains, but they could keep legacy support for old custom domains still under fly.io