You can use a debugging proxy (such as ProxyMan or Charles Proxy) to see outgoing calls coming from your Elixir project. Unfortunately, Elixir doesn't look at your system's proxy settings, so you have to set the proxying manually in your networking library. Here I am using Tesla with Hackney.
use Tesla
adapter(Tesla.Adapter.Hackney, proxy: {"localhost", 9090}, ssl_options: [{:verify, :verify_none}])
# plug Tesla.Middleware.Compression