It is clear that you have not authenticate your app to access the platform.

Read these documentation to learn how to create and app, authenticate and call the APIs

https://developers.ringcentral.com/guide/applications
https://developers.ringcentral.com/guide/authentication
https://developers.ringcentral.com/guide/messaging/fax/sending-faxes

Ask in a different thread if and when you have a particular question.

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