To use the Reverse Contact APIs, you need to sign up here.
Follow the steps below after sign up to obtain the API-KEY for API authentication.
Your API-KEY carry many privileges, so be sure to keep them secure! Do not share your secret API keys in publicly accessible areas such as GitHub, client-side code, and so forth.
All API requests must be made over HTTPS. Calls made over plain HTTP may fail. API requests without authentication will also fail.
After your account is properly setup and you have access to the API KEY, the next step is to use the API Key to make request towards all other endpoint. The API KEY must be a query parameter in all other requests.