Even with the app installed, WhatsApp uses a proprietary protocol that changes frequently. Old clients cannot "handshake" with modern servers. Verification:

(likely version 2.11.x or older). These are often found in community repositories like Archive.org Bypassing Modern Restrictions:

WhatsApp IPA on iOS 6 provides a functional messaging experience for users stuck on older devices or iOS versions. While the installation process requires some technical know-how, it's still possible to breathe new life into your old iPhone or iPad. Keep in mind that WhatsApp IPA on iOS 6 might not receive official updates or support, but it should still provide a stable messaging experience.