post
https://sandbox.signinc.com/oauth/token
We utilize the OAuth 2 protocol to facilitate authorization.
Using the 2-legged OAuth flow, authorization to interact with our API is obtained in a server-to-server exchange of your client_id and client_secret for an OAuth access token by sending a POST request with an Authorization header containing the word Basic followed by a space and a base64-encoded string client_id:client_secret.