HTTPs subdomain

I am running the radzen app on a subdomain, the domain itself has HTTPs, a ssl certificate... through Squarespace, how do I go about setting up the HTTPs through the domain to radzen?

I don't understand your question. How do you want to setup HTTPS to Radzen?

Ok, so right now the Radzen app, (compiled, built) is running on IIS and is accesible through a subdomain. The main domain itself has a ssl certificate and is running a Squarespace site. It should give the ssl certificate for all subdomains. How do I go about setting radzen up with the https that is set up on the domain?

There isn't anything specific to Radzen in this case. I recommend looking for general instructions about setting up HTTPS in IIS.

It seems when I enable HTTPs on the radzen settings I fail to connect to my own localhost:8000, and whenever I put it on IIS I have a crypto issue.

Radzen's HTTPS mode is only used in development and you have to trust the development certificate in order for your browser to open it (or just click "advanced" and proceed). For production you have to install the certificate on your web server.

Ok, I installed my certificates on SSL on ISS, the Radzen app appears on HTTPs but it fails to connect to the C# backend.
On firefox I am getting this error:
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://domain:5000/api/ServerMethods/Add1?I=1

and on Chrome I get
Mixed Content: The page at '<URL>' was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint '<URL>'. This request has been blocked; the content must be served over HTTPS.

It seems the backend is not binding to the https or something? Any tips on this behaviour? I have changed the file to point to HTTPS and port 5000, should I use a different port of some such?