You can use a phone number that is already registered in the Android, iPhone, or Business application versions of WhatsApp. However, in order to register this phone number on WhatsApp Business API, you need to follow the steps below 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.

1. Open the WhatsApp (or WhatsApp Business) application on your Android or iPhone.
   
   
2. Navigate to the Settings page.
   
   
3. Select Account.
   
   
   
   
   
   
4. Select Delete my account.
   
   
   
   5. Follow the steps to delete the WhatsApp account for that phone number. It may take up to 3 hours for the disconnected number to become available. 
   
   
   
   
   That's it! Now simply send your WhatsApp phone number to the MessageBird Support team at support@messagebird.com. We will now be able to register your number directly with WhatsApp, or you can do it yourself by following the embedded signup
   
   Please keep in mind that If you do not perform a backup, you will lose your existing chat history.