What each one actually is
WhatsApp Web is the same browser-based session you use yourself, driven from the server side — there is no extra fee, just a small VPS. The Business API is a paid, official channel with templates, broadcasts and SLA — but you pay per message and you need a partner (Twilio, 360Dialog, etc).
When Web bridge is enough
For a single shop or a small studio that talks to customers one-by-one, the Web bridge handles everything: inbox, replies, delivery alerts, even quick replies. No monthly bill beyond the VPS. The only real limitation: WhatsApp's own anti-spam means you don't blast 500 cold messages from it.
When to move to Business API
Two clear signals: (1) you want to send templated broadcasts ("valentine's preorder open") to a list — Business API templates are the legal way. (2) You add a second operator and want phone-number ownership not tied to one device. At that point the per-message price becomes worth it.
How Acanta is built
Acanta runs both. You start on the Web bridge — fast, cheap, in production. When you outgrow it, you flip a switch and the same inbox works against the Business API, no migration. The conversations and the client cards stay where they are.