If you previously "purchased" an app on a newer device using the same Apple ID, you can often download it directly: Open the on your iOS 9.3.5 device. Go to the Purchased tab.
An is a collection of .ipa files. IPA stands for iOS App Store Package —it is the archive file format that stores an iOS app. Think of it as a .exe file for Windows or a .dmg for macOS. ipa+library+ios+935+free
: A user-friendly database where you can search for apps by bundle ID and minimum OS requirements. If you previously "purchased" an app on a