Remote into Windows PC via iPhone 12 Pro

Hello. First time post. The only way that I can remote into a Windows PC from my iPhone app is if I connect via Tailscale. Entering the RD client ID results in a connection error.

I am able to remote into a Windows PC from my own Windows 11 laptop. No issues there. ID/Relay server appears to be setup properly (I am using a subdomain eg. rust.mydomain.com) Same key entered on all devices. All necessary ports are forwarded in my router at my end. What, if anything am I doing wrong?

Your time and guidance will be greatly appreciated.