A lot of people are getting this Whatsapp error message and getting annoyed by it but fortunately the fix is insanely simple.
The error message is: “Unknown error code during application installation: -24”
Usually it looks like this:

Fix #1: Wipe Google Play Cache/Data
- Tap on Settings
- Tap on Apps
- Find and Tap on Google Play Store or Google Play Store
- Tap on “clear data” button
Fix #2: Wipe Whatsapp Cache/Data
This will delete your Whatsapp downloaded files so make sure they’re backed up.
- Tap on Settings
- Tap on Apps
- Find and Tap on Whatsapp
- Tap on “clear data” button
Fix #3: Remove and Re-Install Whatapp
- Hold down on the Whatsapp app and Uninstall it
- Turn off your phone
- Turn on your phone
- Re-install Whatsapp and log back in
One of these three fixes should have solved your problem!