"The server returned an invalid response" on Pretix-Installation behind Nginx.

[Bapf]

I have a self hosted Pretix installation behind an Nginx as reverse proxy.
Both the web access an the iOS scan app work fine, but when I try to connect this app i get an "The server returned an invalid response" error.

• Pointing the dns entry directly to the pretix server works, so the culprit is definitely the reverse proxy.
• I don't even see any requests on the vhost log on the Nginx. So I suspect the error already happens when the ssl negotiations are taking place.
  Which further information could be helpful?

[raphaelm]

Do you see a request on any other vhost / nginx log?

[Bapf]

If you ask this way ... yes: In the permanentban.log. (I forgot to mention it's an Nginx running inside an OPNsense and I only checked the normal vhost-logs so far.)
Interestingly only the POST-requests from the android app land there / trigger this. Not requests from the web or the iOS app ...

(I'll try to do some further debugging on my side first next week. thx so far.)