What you're trying to do is act as a "Reverse Proxy for HTTPS".
From the Fiddler book
Acting as a Reverse Proxy for HTTPS
One problem with running as a reverse proxy is that the client never knows that its traffic is really flowing through a proxy server. That means that if the client makes a HTTPS request to Fiddler, it does not establish a CONNECT tunnel first, it instead attempts to begin a HTTPS handshake immediately. Fiddler, expecting a HTTP request, will consider the binary HTTPS handshake as malformed traffic and will abort the connection.
This problem can be solved by creating an additional network listener for Fiddler to receive HTTPS connections. In the QuickExec box below Fiddler's Web Sessions list, type
!listen 444 WebServer
This will create a new network listener on port 444 which will expect all inbound connections to start with a HTTPS handshake. Fiddler will act as the server, returning a certificate for whatever hostname was specified in the second parameter to the listen command. In the example above, the certificate would match any request to https://WebServer.
After the secure connection is established, the OnBeforeRequest handler in FiddlerScript may route the inbound secure requests to the actual server. You can examine the oS.oRequest.pipeClient.LocalPort property to identify requests that were sent to the secure listener.
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