Reverse proxy iis10

Hi,

I have bitwarden_rs docker running in a small VM.
I have windows server 2019 running with IIS with letsencrypt certificates with a duckdns address.
I have set up a reverse proxy in IIS to the bitwarden url in the docker image.
But the only thing I get to see is “bitwarden” text with a broken image in front of it.
So I guess i need to add some extra config in the reverse proxy settings.

Does anyone have an idea? Or should I just give up and add nginx to the vm?

thanks