Often times app issues can be remedied by updating your app or iOS. Troubleshooting step number one: Check for updates!
Check for Walla App Updates
Select your phone's App Store icon
Tap your profile icon at the top of the screen
Scroll to the Walla App to see pending updates and release notes. If your app is updated, select Open to start using the Walla App. If your app requires an update, select Update.
Check for iOS Updates
Select your phone's Settings icon
Choose General
Select Software Update. If your phone's iOS is up to date, it will say "iOS is up to date".