So my goal is that you can buy via paypal ingame and then when the buying is complete you get redicted to another level. Is its a way that this can work or any other ide? 
//SLIMEBASS
Here is a complete tutorial on using Paypal for in-game purchases.
http://www.wildbunny.co.uk/blog/2012/03/20/accepting-paypal-in-games/
It discusses both server and client side topics and should get you well under way.
I just released a plugin for a complete license manager in Unity, including PayPal payments, payment-verification, server- and client-code. Unity Asset Store - The Best Assets for Game Making