I had an iPhone 5S before which I sold on eBay to buy the new iPhone 6. I bought this app Super Recorder for my iPhone 5S before, once I jailbroke my iPhone 6 I installed the app and when it opened of course the old activation code was there because I restored from my iPhone 5S backup. Once I opened the app when I tried to activate it pressing the activate button it was saying it can't be activated because it was used on another device. In the app you have the option to reset the code and the system send you an email with the same code you have saying the reset was successful, but when you try to activate it again it keep saying the same thing. I contacted the developer with no response so what I did I used iFile and went to private/var/mobile/media/DCIM/hAcx/ticket.plist and open it with Property List Viewer there you are going to see Ticket, there is where your code is, delete it and save. Reboot your iPhone and open the app again, now your activation code suppose to be empty (if you delete your code from the app is not going to work, that's why you have to do all this), write the code again and press activate, now it will be activated.

Note you have to reset your code first from the app and wait for the auto email response to do this.

This is not a crack for this app, your other device UDID is attached to the code given to you when you bought it, when the system reset the code for you it is releasing the other device UDID and when you activate it again you are attaching the new UDID from the new device you have, this is a solution for the people that bought the app already and have this problem.