Cannot buy apps from App store
First, try restarting your device.

Second, try doing a forced-restart by holding the power and home buttons down at the same time until the Apple logo appears, and then release (this should only be done in desperate times, not as usual practice).

Third, follow these steps: (which can be seen on this site)


Go into the App Store.
Across the bottom, you will see a white bar. 
On the far left, you will see a star and the word "Featured."
Tap the star 10 times. You will see the screen flash white momentarily. 
Restart your device again.


Then try to download the desired app again.