There is also a dedicated Notifications permission that you’ll need to have:
If you’re running your logic with a service-user you would also have to state ROLE_NOTIFICATION_2_ADMIN in your cumulocity.json.
Other than that, Stefan is right…Notification 2.0 is available on all our public cloud instances. For customer-specific instances you would have to check if its activated (there it is activated by request, not by default. See also C8Y Notification 2: getting 404 error).