For example the app lovoo, you can download the app of the day and get 50 coins
Apple has backed off somewhat on incentivized ads after a lot of people put pressure on them. They still have some pretty tight rules, but it’s not as restrictive as it was a couple of months ago.
As far as in-game economy and tracking coins earned during play or purchased from in-app purchases, I’m not sure of a specific plugin for it. Some of the multi-player services like playTogether might have support for it. You can always use a hosted database solution like Parse to have your own cloud store for that information. One of our Corona SDK community developers has put together a site called Coronium (http://coronium.io/) that might be a good solution to tracking your users and their balances.
Rob
Chartboost reply to me, them not allow incetive downloads 
Any alternative?