SSLHandshake: Received fatal warning: certificate_unknown Charles> iOS 10.3
SSL errors on iOS 10.3 and higher
SSLHandshake: fatal warning received: certificate_unknown You may need to configure your browser or application to trust the Charles Root Certificate. See the SSL Proxy section in the Help menu.
This is because iOS 10.3 improves the security of the custom root CA: Just go to Settings> General> About This Phone> Trust Setting and trust Charles to certify
This is due to the new security settings for iOS. To remove the error, you need to trust Charles's certificate. Settings> About> Certificate Trust Settings> Trust Charles Root Certificate (Enable)