Indian small businesses running WhatsApp marketing hit the same wall. The free Business app works until it does not, and the API looks like overkill until it suddenly is not. The threshold is more concrete than most advice suggests.
What the Business app actually allows
Broadcast lists cap at 256 recipients per list. More importantly, a broadcast only reaches people who have saved your business number in their contacts. This second constraint is the one that catches teams out, because delivery quietly collapses as your list grows beyond your existing customers.
You also get no automation, no CRM integration, one device historically, and no analytics beyond delivered and read ticks.
What the API gives you
No saved-contact requirement, template messages at scale, automation, CRM integration, multiple agents on one number, and proper delivery reporting. You also get per-message costs, a BSP relationship, template approval workflows, and a categorisation system that decides your rates.
The threshold
Move to the API when any of these is true. You are sending to more than a few hundred people who have not saved your number. You need messages triggered by events in another system, such as order status or abandoned cart. More than one person needs to reply from the same number. Or you need consent records you can produce on demand, which the Business app does not give you.
Stay on the Business app if your list is mostly repeat customers who have your number saved, volumes are modest, and one person handles replies. Plenty of profitable Indian businesses never outgrow this, and moving early adds cost and process for no gain.
The migration nobody plans for
Moving a number to the API is one-way in practice. Once a number is on the API you lose the Business app interface for it. Teams that migrate their only customer-facing number without preparing agents for a new interface lose a week of response quality.
Run the API on a new number first, move traffic gradually, and keep the old number live during the transition.