error message app download not from app store

Check Apple’s support forums through this link here.Drag Things from the Applications folder to the Trash, then try downloading Things again from your list of previous purchases.Download any free app, and then try downloading Things again.Then go to App Store → Updates to download the update.

Sign out of the App Store (not iCloud) and reboot your device.If it’s not, quit the app and move it there, then try the update again. Make sure that Things is in your Applications folder.If there’s a warning that says “ Unable to Download App. If this didn’t help, proceed with the steps in the next section. Now try updating Things again through the App Store. If you find this, select it and hit the round button with the x in the toolbar at the top (Force Quit).Search for “ThingsWidgetExtension” (search is in the upper-right corner).Open Activity Monitor from Applications → Utilities.Due to a macOS bug, this can make the update fail. If you try to update unsuccessfully (the download starts but just stops and resets), you might have a Things widget enabled.

Error message app download not from app store