Note that if the developer has pulled the older version from the App Store and you don’t have your own archive of the installer in your iTunes library, then yes, your only option will be to update iOS.
You will not be able to get iOS 9 either. The iOS update process only offers you the most current release for your hardware. For an iPhone 6 you will only be able to update to iOS 10.3.3 now.
Note that if the developer has pulled the older version from the App Store and you don’t have your own archive of the installer in your iTunes library, then yes, your only option will be to update iOS.
You will not be able to get iOS 9 either. The iOS update process only offers you the most current release for your hardware. For an iPhone 6 you will only be able to update to iOS 10.3.3 now.
Take a look at this. If there is an older version of the app that you want to download, this may still work for you.
Install an app on an earlier version of iOS or OS X - Apple Support
This similar discussion might be of some interest as well.
I cannot download pages, numbers, nor keynote on my iPad 2 anymore?? Help!!
Thanks I appreciate the advice, looks like I'm updating my ios
Older versions of apps such as twitch and youtube seem to be unavailable for me to download on my iphone 6 which is currently running ios 8. is there anyway to get these apps again without having to download ios 9?
