This application requires iOS 15.0 or later. nis You must update to iOS 13.0 in order to download and use this application.

For the iPhone 6 – introduced nearly ten years ago – iOS 12 is the end of the line.

You cannot update the iPhone 6 to iOS 13.0 or later, nor to iOS 15.0 or later. Thus the iPhone 6 cannot run the apps in question. If you want to run those apps, you will need to buy a new (or at least newer) iPhone.

If you are thinking about buying a used iPhone, you may want to read

The All Too Common SAD Reality of Buying a Used iPad/iPhone – Apple Community

to help you avoid mistakes such as buying an Activation-Locked "brick".

Rakeshkumar67 Said:

"This application requires iOS 15.0 or later. nis You must update to iOS 13.0 in order to download and use this application."

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Updating an iPhone 6 Past iOS 12:

A. You can't.  The iPhone 6 will only install to iOS 12.5.7. See here: Update your iPhone or iPad Software if you're Experiencing Issues with Location, Date, and Time - Apple Support. And, for the note, even if you could update, only the latest version will install.

So, what to Try:

B. Update Using a Computer:

Have a Computer Handy? If so, try using a computer to update. Go here: Update your iPhone Using a Computer - User Tip. If any updates are availabe, they will install, sure enough.

You need a new phone. The iPhone 6 cannot update to iOS 13, 14, 15, 16 or 17.

You need an iPhone 7 to run iOS 15

You need an iPhone 8 to run iOS 16

You need an iPhone XR or higher model to run iOS 17

An iPhone 6 can't be updated beyond 12.5.7, it doesn't have the hardware required to run anything higher.

If you need a higher iOS version, you will have to purchase a newer phone.