Periodically you may try to install/download/update an app in the Mac App Store (MAS) and it may show "waiting" indefinitely. Restarting the Mac App Store doesn't seem to help. If you have a "stuck" download, please try the following:
- Quit the Mac App Store.
- Navigate to /Applications/Utilities/
- Open Activity Monitor.app
- Search for "storeagent".
- Select it, choose "Quit Process".
- When asked if you really want to quit the process, choose "Quit".
- Open the Mac App Store and try to download the app again.