When using Ktor behind a reverse proxy (via Træfik) and using https all my POST requests return instant 403 response. I have tried installed the

XForwardedHeaderSupport

module, without any luck. using HTTP works perfectly fine. anyone that knows why this is? or how I should go about debugging this?

have you installed

HttpsRedirect

? Try it without it - depending on the forwarded headers this might be an issue