yep i am getting the same response for for getting follower, though the docs in no so good conveying this but we need atleast basic tier it seems..

When authenticating requests to the Twitter API v2 endpoints, you must use keys and tokens from a Twitter developer App that is attached to a Project. You can create a project via the developer portal.

{ "client_id": "29610191", "detail": "When authenticating requests to the Twitter API v2 endpoints, you must use keys and tokens from a Twitter developer App that is attached to a Project. You can create a project via the developer portal.", "registration_url": "https://developer.twitter.com/en/docs/projects/overview", "title": "Client Forbidden", "required_enrollment": "Appropriate Level of API Access", "reason": "client-not-enrolled", "type": "https://api.twitter.com/2/problems/client-forbidden" }