You can try out HCSS APIs right here on the developer portal. Choose one of our APIs, select an endpoint, and click the "Try It" button. This will open a panel where you can specify parameters (if any), and send the request directly to our servers.
Since our APIs require OAuth bearer tokens, you will need to add an Authorization header that contains your token. Tokens can be retrieved using client credentials flow or authorization code flow. See Request Tokens.
[Soon] Select "client credentials" from the Authorization dropdown, and we will automatically add a token that points to our public sandbox environment, making HCSS APIs even easier to try.