WhatsApp sends a request to your Facebook Commercial Manager, which you will need to approve in order to configure your WhatsApp Business line.
The request will be under the name MKMB Soluçoes. If you needed more than one line you will see more than one request.
1 - Go to business.facebook.com and then in Business settings.
2 - Next click on "Requests," in the side bar and select "Received."
3 - Accept the request. You will then be able to configure your line.