Not able to start push notifications in settings for whatsapp

Open WhatsApp > Settings > Notifications >

• Message Notifications
• Group Notifications
• In-App Notifications

Check if you have not selected Non of any of the above.

On iPhone

Change alerts

To add or change an alert style for a notification:

1. Go to Settings > Notifications > Check Lock Screen [Ticked]

WhatsApp is not an Apple product. Contact the app developer here --> App Support or WhatsApp FAQ  Or Restoring your chat history - WhatsApp FAQ or Contact WhatsApp