Thanks for that information! Taking a closer look, it seems like the issue might lie primarily with the logs: that 403 response is coming from your app, so traffic is being sent there correctly.
You might be able to investigate further by sshing into your app’s instances (fly ssh console $app-name) to check if there are errors with any listening services with tools like ss and curl.
Restarting the apps’ instances may also be a good initial troubleshooting step for its logs.
I hope this helps point you in the right direction!