Several things to try:
Have you restarted your device? That sometimes clears up odd issues.
If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open, click here --> https://support.apple.com/HT201398
Redownload apps, music, movies, TV shows, and books from the iTunes Store, iBooks Store, and App Store - https://support.apple.com/HT201272
How to contact an app developer - https://support.apple.com/HT207959 - for problems running an app or problems restoring purchases
If you can't resolve the issue:
To "Request a refund for apps or content that you bought from Apple" click on this link --> https://support.apple.com/HT204084