First try to restart the app, and close other apps that might be running in the background on your device. This can be done either by holding the home button and swiping right on any apps that are open, or by tapping the "Recent Apps" button and swiping right on any apps that are open.
You can also try restarting your smartphone or tablet, this can help to clear up some basic app issues. As a last resort, you can try to uninstall and reinstall the app.
Redownloading the app is free once you've paid for it once, so don't worry about any fees.
If you're still stuck and having an issue, please email us at firstname.lastname@example.org and let us know what device you're using, which Dr. Panda title you're having an issue with, and what sort of issue you have. Once we know the problem we can try and work on a fix, if we aren't already.
All of your feedback is valuable to us, so don't hesitate to send us an email and let us know!