Why am I repeated getting a notification that my influence rewards are expired?

During Doomsday if you are taking part and have some influence level (if you occupy plots for example) then you will get a reward of money every 8 hours. If you don't collect them they will expire and disappear after a couple of days. The message lets you know.

Go to the Doomsday Conquest event menu and the Territory Tap and tap on the 'View Rewards' Button. Here you can collect your rewards.