(Please try these first)

Restart your device.
Experience tells us that a hard reset of the device fixes a majority of issues. Note, this is not the same as simply turning the device off and then back on again. To restart the device, hold both the home and power button down simultaneously for around 5 seconds. The screen will go black and eventually the Apple logo will reappear and the device will boot up as normal.

Remove & Reinstall.
If restarting your device has failed to resolve the issue and other applications are functioning correctly, then the next step is to remove and reinstall the malfunctioning application. To remove an app, press and hold on its icon, when it wobbles, click the x in the upper-left hand corner. Then visit the App Store to redownload the app. (Note: all non-cloud application data will be lost).

We recommend all users try the universal fixes to the left first, prior to following any app specific support. If that doesn't fix your problem, please select the app from the list below to go to its dedicated support area.

Make sure you read the FAQs, it's very likely someone else has experienced your problem and that a solution has already been posted. If none of this helps, send us a message from the app's support page and we'll be in touch.