WSS via tunnel return 503

I’m trying to access IPMI KVM via public hostname.

In my tunnel/public hostname setup, I have
ipmi.my.domain => https://192.168.0.10

I can access the Web UI, but cannot use the KVM functions.
https://ipmi.my.domain/viewer.html sends a request to wss://ipmi.my.domain/kvm and returns 503

KVM will will work if I access it via the internal IP 192.168.0.10
Is it my config wrong or the tunnel doesn’t support wss protocol?