The primary hurdle is the phone number verification step. Old versions of WhatsApp often fail to send or process the SMS/voice verification code.
Close WhatsApp completely from the multitasking app switcher. Go to > General > Date & Time . Turn off Set Automatically .
Before attempting the installation, it is vital to understand what works and what does not on older operating systems:
Download WhatsApp IPA for iOS 7.1.2: Best Working Methods and Alternatives
