I would advise you to consider the following: If your app is developed to HELP TO promote this drink - i would strongly advise to forget about Payment system. Also, you called your contest a mockup - mockup is a visual prototype, which includes no coding. And yet, in the brief you write that only 100% ready app will be accepted . Please, clarify that, because your app requires advanced programming and the budget above may not entice good quality programmers.
The way this contest is set up is so that it streamlines the amateurs from the professionals who are suppose to be creative, innovative and best application designers and developers on freelancer.com. if you believe you are in the top 5 on here, you will display your work with confidence that you will win this contest. The "quaranteed" tool does not cover contest holders financially if they are not satisfied with whatever prototype is proposed.