Unable to get updates from Book Store

In the Books app, whenever I check for book updates now, I see several pending updates. But when I try to Update any (or do "Update All") book from the Book Store, I get a popup which says:

The iTunes Store is unable to process purchases at this time.

Please try again later

I've been re-trying daily for about 10 days now. On both my Mac (MacOS 11.0.1 as well as after updating to MacOS 11.1) and my iPad (iOS4.2 as well as after updating to iOS4.3) -- both use the same Apple ID for Media & Purchases.

Somewhat ironically, among the books I'm NOT able to update now are the Apple User Guides for iOS4.3 and iPadOS4.3, etc.

Is it just me (or possibly my specific account), or is this a problem anyone else might be seeing with MacOS11 & iOS/iPadOS4?