Marichi Talks
The free Business App runs on one phone for small teams; the API connects a number to software for teams, automation and scale.
The WhatsApp Business App is a free app for a phone. It suits a sole trader: a business profile, quick replies, labels and a small catalogue. It is limited to the phone and a few linked devices, and it has no proper way to plug in your own systems.
The WhatsApp Business API has no app of its own. You reach it through a platform that gives you a team inbox, templates, broadcasts to opted-in customers, chatbots and an API for your developers. Messages you start are charged per message; the app is free.
A practical rule: if more than two people answer the number, if you need to send reminders or alerts from another system, or if customers message outside working hours and expect an answer, you have outgrown the app. Moving a number from the app to the API is possible, but plan it: chat history on the phone does not move across, so export anything you need first.