Good news! There is a very quick fix, so you will be up + running again in no time. Just delete your app and reinstall the app from the iTunes App Store.
To delete the app, just hold down one of the app icons until they all start to move and a little black x will appear in the top left corner of every app. Tap on the x of the Red Stamp app to remove from your phone. Then go to the app store and install the Red Stamp app again. You will be prompted to type in your Apple ID password when you re-install the app.
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