Error: Invalid_Client
If you are seeing this error, you have created a standalone Safari Web App for Box by clicking "Add to Dock" in Safari while on the Box website. We are discouraging the use of the standalone app because it has caused many issues with access. This standalone dedicated Box Safari Web App must be deleted to fix this error. Box should be accessed using Finder, Safari or a Microsoft Office App.
Delete the app from here: /Users/<<your username>>/Applications/Box.app (delete using command-delete or drag to trash)
Right-click or long-press on the app running in your dock and select "Show in Finder"
NOTE: This is not the main Applications folder, this is your user-specific Applications folder. The folder should look like this, with nothing else inside it:
Once this app is removed, please follow the steps here to Add Box as a Location in Word and Excel.