Hi Mario,
Thanks for reaching out. The error MUTATE_ACTION_NOT_PERMITTED_FOR_CLIENT error is triggered when the attempted operation cannot be performed through the API. Could you please share the complete detailed request and response logs of the call via Reply privately to the author so that I can further investigate the issue. You can find information on enabling logging in the ReadMe of your client library.
Let me know if you have any questions.
Thanks,
Nirmita Patel Google Ads Team