All requests except for the authentication request require an access token.
You can obtain an access token by making a request to the authentication endpoint
(described below) using your API key (obtained here)
as well as the email and password of the agent you want represented by your API requests.
You can then store the access token and pass it to all subsequent requests via the header
X-TGP-ACCESS-TOKEN or as a GET or POST parameter access_token.
You can also view your access token by logging into Textline and going to Settings -> Tools & Integrations -> Developer API.