502 error with blitz

My app currently is getting a 502 error while it is working on my local dev instance. Can you help me to resolve this issue?

502 means our proxy can’t communicate with your app. To troubleshoot this, you should run fly logs and see if there are errors that tell you what’s up.

You should also make sure your app is listening on the right address. Details here: Troubleshooting your Deployment · Fly Docs

It only happens on a post request and not on the main site. The proxy hence works but has trouble with one request.