You can use a phone number that's already registered in the Android, iOS, or Business Application versions of WhatsApp; however, if you add that phone number to your Business Manager, you'll see a "Phone Number is Invalid error". Don't worry, simply follow the 5 easy steps of this article to delete the WhatsApp account associated with that phone number.
Keep in mind that any incoming messages during this time will be queued by the WhatsApp servers and delivered once the registration is successful.
Open the WhatsApp (or WhatsApp Business) Application on your Android or iPhone.
Go to the 'Settings' page, and then click on 'Account'
Select ‘Delete my account’.
Confirm your country code, phone number, and click on 'Delete my account'.
Voilà! Now simply send your WhatsApp phone number to the MessageBird Support team at email@example.com. We'll register your number directly with WhatApp that same day or on the next working day.