Add the following to Web.config for the ASP.NET MVC app (inside the <configuration> block)

<!-- START: Add CORS header for WordPress site so we can dynamically fetch popular users there -->
<configuration>
  <system.webServer>
    <httpProtocol>
      <customHeaders>
        <add name="Access-Control-Allow-Origin" value="https://other.mydomain.net" />
      </customHeaders>
    </httpProtocol>
  </system.webServer>
</configuration>
<!-- END: Add CORS header for WordPress site so we can dynamically fetch popular users there -->

Make sure a <configuration>, <system.webServer>, <httpProtocol>, or <customHeaders> block doesn’t exist already. Better to search for these first and then add the code accordingly.

Save the Web.config file and restart the site from IIS. You can now make a call from https://other.mydomain.net to https://main.mydomain.net/ using JavaScript fetch. For example:

let endpoint = 'https://main.mydomain.net/Snapshot/landing-grid-mobile?count=12'

async function getPopularUsers(url) {
  const response = await fetch(url)
  return await response.json()
}

getPopularUsers(endpoint).then(data => console.info(data))