Obtaining twitter screen names from a list of twitter ids?

Question

I am trying to get the screen_names of the 8,000,000 followers of an account (WHO). To get followers of the account I use get_followers from rtweet package:

who_flw <- get_followers("who", n = 8000000, retryonratelimit = TRUE)

To turn user IDs of followers to screen_names I use lookup_users (). But it only retrieves the first 90,000, while my dataset has 8,000,000 follower ids:

who_flw_data <- lookup_users(who_flw$user_id)

Is there any other method to find the screen names of followers of an account or to turn ids to user names?

Thanks