Just my take but I don’t want click to purchase stuff coming to Spotify. In my opinion this a fail.
I already purchase a family plan for 15$ a month .. last thing I need is tap and click add on purchases.
It's incredibly frustrating and only exists to trick readers into overspending on books.
If you go to the website, you can still buy the books for regular money in addition to credits.
(In addition, the majority of books cost more than 1 credit anyway, so in most cases you are much better off buying via a credit)
It does look like you can buy books on audible.com still. They removed the ability from the mobile app and amazon.com. I wont be surprised if they remove it from audible.com as well.
Usually they'd redirect you to audible.com to avoid any google fees but apparently they stopped that?
I do not have the premium audible subscription though, only plus. Maybe that's why?