In-app purchases usually appear right away, but sometimes there might be a slight delay. In case the gems you purchased have not appeared in the game, please close the game fully, then launch it again. This should help the gems come through.
In case the purchase still does not appear, send us a message via 'Contact us' button in the game and we will assist you further. Please include a screenshot of the purchase receipt (iOS) or the order number of the purchase (Google Play) to the message.