whatsapp is not working and not downloading update

You need to update the iPhone.

👉 WhatsApp requires iOS 12.0 or later.

Check -> iPhone type & iOS version -> Go to Settings -> General -> About.

The last security updates iOS 12.5.6 -> released August 31, 2022, available for: iPhone 5s, iPhone 6, iPhone 6 Plus.

Go to Settings -> General -> Software Update -> Download and Install.

If it is an iPhone 6S you can update the iPhone to iOS 15.6.1, see this Apple article:

iPhone models compatible with iOS 15.6.1.

iPhone models compatible with iOS 15.4 – Apple Support (UK)

You need about 6 GB device storage and good Service & Wi-Fi.

If they are On, turn Off Hotspot & VPN.

Then do the update, see the following Apple articles:

Update your iPhone, iPad, or iPod touch

Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If your iPhone, iPad or iPod touch won’t update

If your iPhone, iPad, or iPod touch won't update - Apple Support

You can do the update via PC, see this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC

Update software on iPhone, iPad or iPod touch in iTunes on PC – Apple Support (UK)

If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support