new to this app but not the game how do you castle in this app?

Either move the king two squares over or drag the king to the rook.

weird, I am sure I have tried both these and it hasn't worked. Frustrating when opponents are castling away.

weird, I am sure I have tried both these and it hasn't worked. Frustrating when opponents are castling away.
Was castling legal when you tried? See link for rules.
https://support.chess.com/article/266-how-do-i-castle
If you're new to the app but not the game, castling is typically done by dragging or tapping the king to its destination square, and the rook moves automatically. Check the app’s tutorial or settings for specific castleapp and rules.