There are three ways a business can be on WhatsApp. The normal WhatsApp app on a phone. The free WhatsApp Business app, also on a phone, with a catalogue and quick replies. And the WhatsApp Business Platform, which Meta also calls the Cloud API. The third one is the only one where software can send and receive messages on your number automatically, around the clock, without a phone being involved.
What the official platform gives you
Your business gets its own WhatsApp Business Account with Meta. Your number is registered on it, your business is verified with a government document, and your business name is shown to customers. Messages come to a server you or your partner runs, which can reply in under a second, ask questions with buttons and lists, send reminders at a set time and hand a chat to a human when needed. Meta publishes the rules and the prices, so nothing is hidden.
What unofficial tools do instead
Many cheap automation tools work by pretending to be a phone. They scan a QR code with your WhatsApp app and then control it through the web version. Meta's terms forbid this. The usual result is a ban: the number stops working, sometimes after weeks, sometimes within a day, and every customer who saved that number loses the way to reach you. There is no appeal that reliably works. Any number that matters to your business should never be put on such a tool.
The trade-offs
The official platform has rules. Messages you start must use templates that Meta approves first. Marketing messages need the customer's permission. Meta charges per message for the reminders and offers you start. Your first 1,000 replies each month to customers who message you first are free, and after that Meta charges for replies per message too. In return you get a number that cannot be banned for automation, a verified name and the ability to answer every customer in seconds, which is the whole point.
What you need to get on it
A Facebook account to create a business portfolio, a document that proves the business is real (an Udyam certificate or a GST certificate works), a phone number that is not currently on the WhatsApp app, and someone to build and run the replies. Dunnflow does the building and the running; you own the account, the number and the data.