@sudha0618 as the error messages indicate, you can only target the followers of user who have gone through the process of becoming a promotable user for your advertiser account. Currently your advertiser account has no promotable users except for yourself, the owner of the account which is by default a FULL promotable user.
For a list of promotable users available to you, you can call GET accounts/:account_id/promotable_users.
It’s by design that you’re not able to make these calls or target a user ID that your account isn’t eligible to promote. Under the hood, both the UI and the Ads API share the same common back-end where this intentional restriction is enforced. While the UI might enforce it a bit father downstream, you’ll still not be able to do what you’re attempting to do in either system.
