That's probably because the app. itself's needed to be updated, the same as the update in our other app. (Like Whatsapp that needed to be upgraded every now and then. You don't always hafta do it right away, but at some point it became necessary.) And our phones automatically sent us to the AppStore (or google store in android) to upgrade it.

The problem is that GBF is region-locked, so if your phone's region is not set to Japan (which I'm sure isn't), it won't show up in the store.

The solution? The easiest ones are pretty much the same as above, either use Skyleap or Chrome. Though if really want to play in-app, you can try using a third-party store, such as Qoo-app.