There’s a “games & rounds” section for things like this... It’s much more convenient there and keeps this ANN page much cleaner and nicer. So maybe you can move this giveaway there... just a suggestion.
OP has told the users to send a message to him to get the bonus, which is okay. But some users are posting their usernames in the ANN thread, it is against the pinned post rule of gambling board. OP shouldn't credit the bonus to those users who are posting their usernames here.
By the way, 500 people getting $10 each is quantity, while 25 people getting $250 each would be quality.
Maybe they are looking for the quantity. Even giving $50 to 100 users will bring some quality here. They can run a review campaign here with this reward amount.