RequestBin is a great tool for testing your API code. It lets you create your own personal "Bin" (as in "rubbish bin", not "binary"!), send test HTTP requests to it's unique URL, and then inspect exactly what your code sent.
It's very helpful for when you think your code should be sending the right thing, but you're not getting the expected result.
Go to requestbin.com in your browser, and Create Request Bin. You can create an account with PipeDream, or you can click public bin below, which will create a publically viewable request bin.
You will see that RequestBin gives you a URL to call: "Your end point is...".
Replace the URL of the WhatIsMyBrowser.com API with that URL and then run your code. You should see the request/s start to appear in the Request Bin you created, instead of being sent to the API.
You can then inspect the requests that your code is sending, to see exactly what you are transmitting. This is helpful to find if the auth header isn't being sent correctly, or if there's some issue with the JSON.
Hopefully Request Bin helped you identify the problem with your requests. If it didn't, you can contact us and we'll see if we can spot the problem for you.