The official Facebook app requires iOS 10, 11, or later to run. If you try to download Facebook from the App Store on a device running iOS 9.3.5, you will get an error, or it will attempt to download a version that simply crashes or refuses to install.
Once you find a verified file, you cannot simply "open" it on your iPhone or iPad. You will need a sideloading tool. facebook ipa for ios 935 verified
I can provide a step-by-step guide for the method that fits your situation best. The official Facebook app requires iOS 10, 11,
If the sideloading process seems too complex, consider these workarounds: You will need a sideloading tool
A: You likely downloaded a version built for 64-bit (iOS 10+). For iOS 9.3.5 (32-bit), you specifically need an IPA compiled for armv7 architecture. Facebook v78.0 through v84.0 are the only stable ranges.