It ended up being the "Format" field under the "Regional" settings.
Doesn't matter that my primary language, display language, and even over-ride system language are all English, the Beta Store looks at the "Format" field. This one:
If it's not set to "English (United States)" the beta store will not function correctly!
Once I changed that to "English (United States)", closed and reopened the store - everything started working smoothly.
Changed it back to "Hebrew" as it was before - store stopped working - install button became unresponsive.
I found this via the windows event viewer, where I found this error:
DownloadUrl failed - 404 for https://displaycatalog.md.mp.microsoft.com/products/9WZDNCRFJB9S?market=neutral&language=he-IL&fieldsTemplate=Full Function: DownloadUrl Source: The parameter is incorrect. (enduser\windowsupdate\client\installagent\dll\httphelpers.cpp)
So I realized it had to be picking up the "He-IL" string from somewhere, and the only place I had it set was the "Format" field above (which usually doesn't affect apps)
Not sure about other regional settings (As I have them all set on English (United States) already) but you might wanna look into those settings if you're still having issues.
"Teach thy tongue to say, “I do not know,” and thous shalt progress." –Maimonides
Did this solve your problem?
Sorry this didn't help.
Great! Thanks for marking this as the answer.
How satisfied are you with this reply?
Thanks for your feedback, it helps us improve the site.