Authenticating your API requests is done by sending a HTTP Header called: X-API-KEY, with the value being your API Key which you got by following the Get your API Key instructions.
Here are some relevant snippits of sample code showing this to give you the idea.
As per the HTTP RFC 2616, header field names are not case sensitive, so it doesn't matter if you send the header as X-API-KEY or x-api-key.
For examples in more programming languages, please look at our Sample Code.
If you don't send the your API Key in the X-API-KEY HTTP header, you will receive a response like:
This will happen if you haven't sent the authentication header correctly. Check out the section on Debugging Authentication.
If you send an incorrect X-API-KEY, you will receive a response like:
Note that the API Key that you sent through is included in the result message; so that you can confirm that you are sending the key that you intend to.
This error can occur if you generate a new API key but don't update your code to send the new API key through, or if you have incorrectly copy and pasted the key.
If you're stuck, check out the section on Debugging Authentication.