The official platform needs a number that is not currently registered on the WhatsApp app or the WhatsApp Business app. A number can only be in one place. So the first decision for every business is: which number.
Option one: a new SIM
A prepaid SIM for ₹100 to ₹200, kept in a drawer after the one-time verification code. The number becomes the business's WhatsApp line, printed on the board, the visiting card and Google Maps. Existing customers get one message from the old number pointing to the new one. This is the cleanest option and what most businesses choose.
Option two: move the existing business number
If the business already uses a dedicated number on the WhatsApp Business app, it can be moved. The chat history on the phone is kept as a backup, the number is removed from the app, and then registered on the platform. From then on, the owner reads and replies through the assistant and their own personal number, not through the app. It takes about an hour and Dunnflow does it with you on a call.
What not to do
Do not use the owner's personal number. It would have to leave the WhatsApp app, and the owner needs their own WhatsApp to receive alerts, take over chats and read the daily summary. Do not use a number that was recently used by someone else; Meta sometimes refuses recycled numbers until the previous WhatsApp account on it is deleted.
Landlines
A landline can be registered too, with a voice call for the code. Customers do find a mobile-looking number more natural, so a SIM is still the common choice.