Make sure the barrier isn't impossible to get through. Some common barriers include:
A "water fall" where you have to fall down a large strip of water while dodging objects such as Spikes, Sharks, etc. A "dirt run", a long area made of dirt you have to run through before you reach the prize. This adds some resistance to having all the prizes taken by winners very quickly, allowing you to stock up easily. Try not to make it too long, otherwise players might get bored and leave. A "password door" area is another option. Don't make it an impossible answer; do something simple like 1-10, or ask easy questions like "What's the owner's name?".
If you make up some crazy question like "1-500", it could be pretty easy to identify your world as a scam, even if the answer is something that is really between one and 500 because it takes a very long time to guess and players won't have fun typing in a ton of numbers over and over. This also applies to other impossible questions, such as "What is the owner's favorite animal?" with absolutely no hints whatsoever.