App Store won't update I'm trying to update Airmail to the latest version on my MacBook with El-Capitan 10.11.6 (15G31).

When I go under App Store > Updates, I see no new updates. When I search for the Airmail app I see that I am 1 version behind. If I click the "update" button, all I see is the progress indicator spinning for hours.

I've tried:


Restarting my Mac
Clearing App Store cookies
"Reset Application" in App Store
Running killall -KILL storeagent (which says No matching processes belonging to you were found)
Running Disk Utility to check for any problems (none found)


How can I restore my ability to update apps?
Ultimately, I had to delete the Airmail app and reinstall it entirely. It's now able to update.

The problem appears to be due to the fact that when Airmail 2 was upgraded to Airmail 3, the internal app version was 3 while the version shown in the Applications folder was v2. I think this confused App Store.