when are you using it? here are the instructions on how to use it:
Nudge
Players can be 'nudged' if they don't play their turn after 24 hours. This will send the player an e-mail notification informing them they are holding up a game.
Each player can only be nudged once every 24 hours across all of their games. This prevents a player who is away from receiving multiple nudges.
is your use aligned with this? are you trying to nudge too soon? did someone else already nudge first?