Click Tools > Fiddler Options > Connections.
Click the checkbox by Allow remote computers to connect.
Ensure your firewall allows incoming connections to the Fiddler process, and that it's not blocking all incoming connections, including those in the list of allowed apps.
Hover over the Online indicator at the far right of the Fiddler toolbar to display the IP addresses assigned to Fiddler's machine.
Verify client iOS device can reach Fiddler by navigating in the browser to http://FiddlerMachineIP:8888. This address should return the Fiddler Echo Service page.
For iPhone: Disable the 3g/4g connection.
Tap Settings > General > Network > Wi-Fi.
Tap the settings for the Wi-Fi network.
Tap the Manual option in the HTTP Proxy section.
In the Server box, type the IP address or hostname of your Fiddler instance.
In the Port box, type the port Fiddler is listening on (usually 8888).
Ensure the Authentication slider is set to Off.
Download the Certificate Maker plugin for Fiddler.
Install the Certificate Maker plugin.
Configure the device where Fiddler is installed to trust Fiddler root certificate.
On the iOS device, go to http://ipv4.fiddler:8888/ in a browser. Do this from Safari, Chrome will just download the certificate and will not offer to install it, the same for Firefox.
From the bottom of the Fiddler Echo Service webpage, download the FiddlerRoot certificate.
Click Allow to download a configuration profile.
Go to Settings > Profile Downloaded, tap the downloaded DO_NOT_TRUST_FiddlerRoot profile, click Install.
Tap the Install button again, and confirm with yet another Install button.
On iOS 10 and later, after installing the FiddlerRoot certificate, go to Settings -> General -> About -> Certificate Trust Settings and manually enable full trust for the FiddlerRoot root certificate. Accept the dialog that says that this will allow a third-party to eavesdrop on all your communications.
If you decide to uninstall the root certificate:
Tap the Settings app.
Scroll to Profiles.
Tap the DO_NOT_TRUST_FiddlerRoot* profile.