If you have to use Zscaler, for example to access a corporate network, you may run into issues and need to debug your problem. This article gives a high level overview of how the 2 tools work together
How the tools work together
Charles uses the “External Proxy settings…” tool to forward Charles traffic to an another/external proxy, in this case Zscaler
External Proxy settings
Open External Proxy settings
Open Proxy -> External Proxy Settings…
Verify the “Use external proxy server” is enabled
View Zscaler proxy settings
“Web Proxy HTTP” and “Secure Web Proxy HTTPS” should both be enabled
These host and port settings (127.0.0.1:32700) are used to forward traffic to Zscaler
NOTE: your port value may differ from this example.