rest_cannot_update error

The status code 403 (Forbidden) in the response suggests that your request is not properly authenticated.

You could start by reviewing the REST API handbook section on Authentication, in case there’s something you may have missed, and double-checking the credentials, if any, you’re using with to make the request.

You can also pass auth_callback as one of the $args to register_meta(), if you need to customize the meta update capability checking.

auth_callback – A function or method to call when performing
edit_post_meta, add_post_meta, and delete_post_meta capability checks.

Or contact the plugin author’s customer support as Chris Cox mentioned in the comments.