WhatsApp officially dropped support for iOS 9 in February 2020 . This means you can no longer create new accounts or verify an old phone number on iOS 9. However, if you already have an active WhatsApp account on a newer phone, you can trick the App Store into downloading the last compatible version (version 2.20.30).

Once the QR code appears, scan it using WhatsApp on a newer primary phone to link the devices. 3. Advanced/Community Methods Whatsapp Ipa For Ios 9.3.5 Download - Google Groups

The interface will look like WhatsApp from 2020–2021 — green top bar, old emoji style, but still functional.