About IOS update

"About IOS update: I already updated my IOS to the latest version but when I tried to download the Facebook it says that I need to update my IOS to 13.4 Orr higher but I already updated my IOS to 15.7.1 How can I fix this???"

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For futre reference...

Updating an iPhone:

What to Update: Update Installed Apps along with the iOS.

Determining if an iOS Update will Install:

How to do so...

I. Verify Compatibility:

Identify your iPhone model. The first thing that comes to mind in incompatibility being the culprit. So, confirm the model of your iPhone. If iPhone model is incompatible with iOS15 then it is because you iPhone does not meet the hardware requirements for this iOS version(s).

II. If Compatible...

1. Back Up First:

IMPORTANT: If you have an option to update, however, then be certain you backup your iPhone first. That way, you will have something to restore your iPhone from should anything go wrong with the update

then...

2. Proceed with the Update:

Use my User Tip:  Update your iPhone Using a Computer - User Tip

Your profile still says you are on iOS 13.