If you want to debug HTTPS requests, you must execute, at any point of your code, these command:
ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
Then, you must add the following lines to your web.config:
<system.net>
<defaultProxy enabled="true">
<proxy proxyaddress="http://127.0.0.1:8888" bypassonlocal="False"/>
</defaultProxy>
</system.net>