How to update the what’s app by payment I want to add a card

See -> If you can’t download or update apps on your iPhone or iPad

If you can’t download or update apps on your iPhone or iPad – Apple Support (UK)

see point 3.

The first time you use the App Store, you need to supply a payment method, even if the app is free, also make sure that you spelt the name of the app correctly and that you are not purchasing a premium version.