First, you submit an authentication request to https://auth.listrak.com/OAuth2/Token with your client id and client secret. If that is successful, you receive a bearer token to use in further API calls. Once authenticated, we need to process a REST API call to https://api.listrak.com/email/v1 with encoded data (ie. email address, etc). I don't know what should be flow, currently I am running my script in the "addtional checkout", but it throws an "Cors" error as attached in the screenshot.