Not able to use Facebook app on iPhone

Start by following Apple's troubleshooting at If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support

If you still have an issue, you then need to use Facebook's support for further help. Facebook Help Center

Estherluv33 Said:

"Not able to use Facebook app on iPhone: Have not been able to use my Facebook app on my iPhone"

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Getting Facebook App to Work on an iPhone:

Meet Sytem Requirements:

Note: This app now requires iOS 13.4 or later to work.

What's your iOS Version:

1. Go To: Settings
2. Tap: General
3. Tap: About
4. View: second item down

So, if compatible...

Reinstall the App: Remove the Facebook app, and then add it back. Get it here: Facebook on the App Store