Subdomains with Ports don't work

I am trying to create a subdomain for my NodeRed interface through Cloudflare Tunnel.
When i enter my servers ip and port 1880, which node red is running on everything works as expected.
But when i want to acces it through the subdomain i have given out through Cloudflare Tunnel it shows an error screen saying “The web server reported a bad gateway error.”
This also not only seems to be limited to NodeRed but to every subdomain i create, that has a port specified
Can anybody help me there?

same problem here. if you find a solution let me know also, please.