This means there are no healthy app instances to route requests to. In general, this could be because your Machines are failing their health checks or they’ve each reached their hard limit of concurrent requests (or connections) set in fly.toml.
I poked at your app and noticed you had–and then removed–your health check in fly.toml. Despite this, I still see old health check data persisted on our end, and your checks were last in critical state before they were removed.
What I think is happening here is a bug: our service discovery system is still holding on to your app’s once-failing health checks. This stale state would then cause Fly Proxy to view your app as unhealthy and stop routing requests to it.
The stale state should only apply to existing Machines. New ones should be created with a clean health check slate.
Try cloning a new Machine with fly machine clone <id>, wait for it to start, and then ping your app again. If your new Machine’s responding to requests, you can destroy the old (possibly stale) Machines using fly machine destroy <id>.
I hope that helps!