To receive your bonus, simply send a PM.
Better watch out for abuse from cheaters, and I would update rules limiting this offer only for higher ranked active members.
Second thing you can do is not allowing users with negative ratings in forum to use this bonus offer.
$5 is not a lot of money but it can be a lot when you multiple it many times.
That's right. There are many users who try to take these bonuses using multiple accounts. Giving bonuses to accounts with a minimum rank would be the right decision to deter cheaters. So they need to take effective action to stop the cheaters that you have suggested. This will allow real players to play in their website which will be effective in their business.