This is because Wear OS build with Watch Face Studio powered by Samsung with an API of 28+, are not supported by Google Play on some 13,840 Android devices.
Customers affected by this error message are advised to browse and download via web browser from personal computer or search the watch name in Play Store > under ‘This Device’ > select Watch and tick their model > proceed to Install > Redeem Coupon > Pay > wait for app to appear on their watch.
I believe Google Play is working on it. In the meantime, Publishers/Developers familiar with Android Studio have paired their apps with another companion app to defeat Google Play’s algorithm (sort of) to project the app through.
Yes, it takes a few days to find the Watch Faces in the different categories. But this has nothing to do with the error that the watch faces are not downloadable.
I have tested this many times on Samsung S9 Plus and Samsung S20 Plus.
I cleared the Play app cache. Watch Faces that were previously discoverable were no longer discoverable.
It seems that you have to click the link twice for the Play app to allow a download.
This error does not occur on a PC browser.