Can’t access IBM Tone Analyzer API?

I’m trying to use the Tone Analyzer API in a Laravel application. No matter what I try, I always get the same response of {"code":401, "error": "Unauthorized"}. I suspect my issue is that I can’t figure out how to pass in the API key, but the official documentation is no help whatsoever because it only contains instructions for using cURL in the command line. My code currently looks like this (though I have tried many many other iterations. If anyone needs me to I can post all the other unsuccessful attempts as well):