How to clear App update flag?

I'm running ios 11.3.1 on an iphone 7 and use Omnifocus. On May 25th Omnifocus posted an update 2.22.4 to the app store. I went to update the next day and got a message "This update is no longer available." Five days later my phone is still telling me there's an update for me but I still get the same message. The App Store icon on my phone continues to have a little red circle on it indicating one update available and I'd like to get rid of the red circle but I don't know how. Is there a way?