[Xymon] Change host using httphdr

I'm trying to access an internal ressource - trying to change the host information in the http header.

192.168.29.11 <http://s.bl-1.com/h/c4MTgLWp?url=http://192.168.29.11> internal-host.eu <http://s.bl-1.com/h/c4MTgRvr?url=http://internal-host.eu> #conn https://internal-host.eu <http://s.bl-1.com/h/c4MTgWJt?url=https://internal-host.eu> httphdr="Host: external-host.com"

I end up with a 404, as the host isn't reconized. Any suggestion on how to imporve?

Regards Leif