iMovie on Macbook download fail: "We could not complete your purchase." What could I do? This MacBook Air 2017 has been freshly installed with Mojave. I wiped the disk before doing so.

After that, I went on to the App Store to download iMovie... but it won't download! The error message displayed above, and "cancelled" inside the popup box, was all the info given. What could this be? I tried deleting App Store preferences, cookies, restarting the computer, changing DNS to 8.8.8.8, changing wi-fi, but none worked.

Also, the download button was a cloud with an arrow, not the usual "GET" button.

I have signed in with the same Apple ID as last time- both for my iCloud and App Store.

Please help!

EDIT: Even other apps won't download. This problem is not specific to iMovie.
Appears to be an issue with the Mac App Store. See this Apple Discussions link: https://discussions.apple.com/thread/251378763