I can’t add or find my friends even if I enter their UID correctly.?

Check if you and your friends are playing in the same region. The game doesn’t support cross-server play.

For example, if your account is in the US (UID starts with 600) while your friends are registered in Asia (UID starts with 800) you won’t be able to find each other or play together. Check out more information in our dedicated page for this topic:

https://www.appgamer.com/genshin-impact/strategy-guide/how-to-cross-save-and-cross-play-work-in-genshin-impact