Unable to reverse proxy on Synology NAS

I have some problem with accessing my HAOS. If I forward the port directly using http, it works fine. If I forward the port to my Synology NAS in https, and use Synology reverse proxy to the http port on HAOS VM (for added security using Synology’s certificate), I got “400: Bad request”. Exactly same settings works just fine with my Pi and other devices… Is there anything I did wrong?

Please refer to this post. It is step by step guide how I configured reverse proxy on Synology, hope ypu find missing piece.

The only thing we did differently is that custom header (though I only use HTTPS connection). I’ve tried it, but it still returns 400… No idea why…

ok… apparently I didn’t know HAOS has internal http control that would block reverse proxy if not configured… Now it’s working. Thanks!!