Your Postgres disk filled up, this is why Postgres is not accepting connections.
You can try expanding the volume (fly volumes extend · Fly Docs), you’ll need to use fly volumes list -a your-postgres-app to get the list of volume IDs. Then you’ll likely need to restart your Postgres machines with fly machine restart (for each machine ID in fly machines list -a your-postgres-app).
I don’t guarantee Postgres will automatically recover when you do this - it doesn’t like it when the disk fills up and it might be unrecoverable. If that’s the case, you’ll likely need to create a new Postgres cluster from a backup and update your main app to connect to the new Postgres. But it’s worth trying the volume expansion first.