Controller is firing but I can't get the $_GET

If i read this documentation correctly the parameter for send is ignored for GET requests. You probably need to do a POST request.

That's indeed correct. Or add the variable into the url, to get GET working.

My understanding is that Post is a one way path from the browser to the server.

No, you can send back information with any method.

Getting the data:
https://www.codeigniter.com/user_guide/l...put-stream

Send back JSON.
https://www.codeigniter.com/user_guide/l...ntent_type