This is a permission issue happens when you call an API of an application that doesn't have that specific permission.

Check the following:

• You are calling API of right application.
• make sure that application you are calling have [Faxes] permission

This literally just happened to me with another application leveraging the [RingOut] permission. I'd mistakenly used an existing app in the sandbox that lacked that permission and saw the same error.

The fix is to:

• Go into your account
• Select the app you're trying to use
• Click Settings in the list on the left-hand side
• In the OAuth Settings towards the bottom, add the [Faxes] permission
• Click Save

This worked to solve my immediate problem and might also help with yours.