A lot of APIs will use an API key that is sent in the request header. The API key could be called anything, depending on the API you are using. It might be labelled ‘api_key’, ‘apikey’, ‘key’, ‘x-api-key’ or whatever the API decides to call it.
This is very simple to achieve using WPGetAPI. You simply need to add your API keys details into the ‘Headers’ section within the WPGetAPI plugin, as shown below. This will then automatically create the correct request headers for you.