Every call call you want to make to the api request that you send the client api key and the client api domain. Those key can be found under the admin configuration information. Those keys can be send either as a url parameter (in case of GET operation):
or as HTTP header :
If both are send, the information in the HTTP Header will prevails.
To test your keys we created an endpoint : Validation
If you need more support you can contact us at : email@example.com