Hi Subain
Thanks for reaching out. The AuthorizationError.USER_PERMISSION_DENIED occurs when there is no link between the manager account authenticated in the request and the client account specified in the headers. Please make sure there is linking between the MCC authenticated and the customer account requested.The problem could be that the OAuth2 credentials you used to authenticate the API calls are not generated from the email address which has the Admin access to the manager account of the customer account. Could you please make sure that the OAuth2 credentials are generated by the manager account and give it a try? If issue is persist, could you please send me the email you used to generate the OAuth2 credentials? Please reply privately to author options while sharing the details.
Thanks,
Nirmita Patel Google Ads Team