Family sharing on IOS

Hi everyone,
I recently purchased Litchi on my iPad using my personal account, and I’d like to share it with my brother on his iPad and account. According to the information on the iOS App Store, Litchi supports Family Sharing. My brother is already part of my Family Sharing group on iOS, but he is unable to download the app. On the App Store, it asks him to pay for the app instead of allowing him to download it directly.
How can we resolve this issue?
Thank you!

It should work. Have you following these instructions?