Facebook API /{ad-account-id}/assigned_users with message: The user ID provided is not business scoped. Please provide a business or a system user ID

Question

I'm working on Facebook Grapth API. Following up on this page. I use the correct ID but they response that The user ID provided is not business scoped

I know the user param is a business user id. Then I tried to get the user_id by this api:

To make sure it's a business user id, I did another request:

And then, this was the result when I tried the request to add user to the ads account