How to fix IIS 10.0 Detailed Error = 404.19 - Not Found shown when posted link on Facebook/META

Use the Facebook Debugger tool to see how Facebook views your page: https://developers.facebook.com/tools/debug/

Ensure your firewall isn't blocking Facebook's IP ranges.

If your web.config includes restrictions on certain file types, you may need to adjust them to allow the resource Facebook is trying to access.

I received a response from DiscountASP.net. I just had to add the following to the web.config to fix the IIS config:

<system.webServer> 
  <security>
    <requestFiltering>
      <filteringRules>
         <remove name="facebookexternalhit" />  
      </filteringRules>
    </requestFiltering>  
  </security>  
</system.webServer>

The first time I tried this it did not work. However, I emailed support and they explained THEY had to fix it "at the root." So, fwiw I bet this works, but in a shared hosting environment, you may need to put it in the server's web.config, possibly replacing the rule name to what's appropriate for your hosting provider.