Sometimes this happens, whether it be from an update on the app itself or an update on the phone - but have no fear! It's usually a pretty easy fix.
The first thing we recommend doing is to restart your device.
If restarting the device hasn't worked - try reinstalling the app.
If that STILL hasn't helped, send us an email to firstname.lastname@example.org with your device model, version of OS (Android or iOS), and a description of the problem.