As of today, even with a successful installation and a bypassed expiration screen, getting messages to send and receive is rare. WhatsApp's modern backend uses end-to-end encryption protocols that the iOS 6 versions simply don't understand.
Installing a WhatsApp IPA on iOS 6 is a fun weekend experiment for hobbyists who enjoy the "Aero" aesthetic of classic iOS. However, it is no longer a viable way to communicate. If you need a functional messenger on an iPhone 4 running iOS 6, you might have better luck with Telegram via the "TelegramLegacy" project or using web-based alternatives. whatsapp ipa ios 6
However, the community around "legacy iOS" has developed various workarounds to keep these devices functional. Methods to Get the WhatsApp IPA As of today, even with a successful installation
The biggest frustration after installing the IPA is the "This version of WhatsApp has expired" message. Because the app is hardcoded with an expiration date, it will refuse to open. However, it is no longer a viable way to communicate