Due to Apple's strict code-signing certificates, you cannot modify app internal files or permanently run expired legacy apps on iOS 7.1.2 without a jailbreak. For iOS 7.1.2, tools like Pangu7 or GeekSn0w are commonly used to achieve a untethered jailbreak.
If you are determined to try, you will need a legacy (specifically version 2.18.80 or older, which was the last semi-compatible version). Method A: Using a Sideloading Tool (No Jailbreak) About supported operating systems | WhatsApp Help Center
Telegram is more friendly to old iOS versions. You can download from your App Store’s "Purchased" tab (if you downloaded it before). Telegram still supports older clients longer than WhatsApp.
: Older app versions (like v2.18.81) cannot connect to modern WhatsApp servers, resulting in connection errors or "version expired" prompts.
The realistic options for using WhatsApp on iOS 7.1.2 are extremely limited, risky, and offer a poor user experience. They are only listed for completeness and are not recommended for average users who value their data and privacy.
Official support now starts from iOS 15.1 (as of May 2025). 2. How to Install WhatsApp IPA on iOS 7.1.2
