In order to use the Betting API, you need to have an Application Key. The Application Key identifies your API client. For the Developer Preview, we have assigned a single key to a preview customers.
You must pass the Application Key with every HTTP request. You do this by setting the HTTP header with the value of the key assigned by Betfair.:
You can create an Application Key for your Betfair account using the createDeveloperAppKeys service.
X-Application: "APP_KEY_ASSIGNED"