Currently, we do not offer an API to check if a user's phone number is WhatsApp enabled.
WhatsApp requires businesses to collect an active user opt-in to message them via WhatsApp. This should serve as knowledge that the user has WhatsApp installed on his/her phone.
🚫 Sending a WhatsApp message to a phone number that is not WhatsApp enabled will fail and fallback to SMS.
ℹ️ Check more information on how to collect opt-ins here.