How to downgrade your number from WhatsApp Business API to WhatsApp BusinessApp
If you are using the WhatsApp API and you want to go back to regular WhatsApp, you can downgrade the number under your Facebook business manager. Downgrading the WhatsApp business API number does not imply the deletion of WhatsApp or the WhatsApp business app.
The API number cannot be deleted until 30 days after the last paid message was sent. Once the number has been deleted, it can be used again in the regular WhatsApp app, or you can register it again in the WhatsApp API.