For the most secure experience, always use official channels to avoid security risks. Google Play Store : The easiest and safest method. Search for WhatsApp Messenger Official Website
Here is an informative guide on the current status, risks, and methods for downloading WhatsApp on Android 6.0.1. download whatsapp for android 6.0.1
The APK architecture does not match your CPU (e.g., you downloaded an arm64 APK for a 32-bit phone). For the most secure experience, always use official