- it must be that king’s very first move
- it must be that rook’s very first move
- there cannot be any pieces between the king and rook to move
- the king may not be in check or pass through check
If you post the actual game link, I can take a look at it. However, I suspect one of the conditions above are not met.
I have tried so many times and I can't do it in this game. Can someone please advise how?