Can you explain more about what you want to achieve?
1. Do you have a RingCentral developer account? If not, sign up to get one. 2. "... using demo developer credentials..." did you mean using the sandbox account credentials? 3. "... using RingCentral credentials ..." did you mean using the production account credentials? Follow the instructions at Apply for production 4. If you have problem with using an API, let us know the API name so we can help.