I don't know if anybody else is experiencing the same issue but at least on the iPhone 6 Plus I cannot download free apps from the app store when running iOS 9. You tap "get" and it turns into "instal" but after clicking instal it switches back to "get".
I don't know if there is a fix either, but if anyone has any idea what's going on let me know.
These issue seems to be ongoing at this time. Some apps/configurations seem especially likely to be affected, but if you try repeatedly they might download.
Seems like a random error with the App Store servers. Hopefully this is fixed soon. Unfortunately this is not properly indicated on Apple's system status pages, so the only way for now is to keep trying or submitting bug reports.
https://developer.apple.com/system-status/
https://www.apple.com/support/systemstatus/
If anybody has other information, hinting that indeed developer action is required to fix this, please reply.
