In order to call this API endpoint, user needs to have [ThirdPartyAppAccess] permission.

What API did you attempt to call?

You can check more information on this ThirdPartyAppAccess permission by calling this API:

GET /restapi/v1.0/dictionary/permission/{permissionId} 
GET /restapi/v1.0/dictionary/permission/ThirdPartyAppAccess

The response indicates if you need to enable the "Third Party Apps Access" permission for the user's role in the RingCentral Online Account Portal

ref: https://stackoverflow.com/questions/51833540/ringcentral-invalid-client-thirdpartyappaccess-permission-required-error

more info on ThirdPartyAppAccess: https://success.ringcentral.com/articles/RC_Knowledge_Article/5-10-Editing-the-Extension-Permissions-via-Web