If you want to test the API in our Sandbox environment you will need to obtain a Sandbox API key, set the API key to that API key, and include a header variable named "X-Environment" with a value of "sandbox" in your requests. We will do that for you here, in the "Try it out!" feature, if you check the "Use sandbox" checkbox above. You will see the header set in cURL command and in the "Request Headers" section of the response if you view the request in your browser.