I am trying to configure Azure application gateway WAF with a backendpool set to a VM in a different Azure tenant using its public IP address on port 443. All the SSL certificates are configured properly. However, I keep getting following error while browsing the site via WAF.
502 - Web server received an invalid response while acting as a gateway or proxy server.
I have confirmed that NSG is on the mentioned backend VM is allowing all traffic on port 443. What could be going wrong here?