Connect WhatsApp via credentials

Connect a WhatsApp Business Account by providing Meta credentials directly. This is the headless alternative to the Embedded Signup browser flow.

To get the required credentials:

1. Go to Meta Business Suite (business.facebook.com)
2. Create or select a WhatsApp Business Account
3. In Business Settings > System Users, create a System User
4. Assign it the whatsapp_business_management and whatsapp_business_messaging permissions
5. Generate a permanent access token
6. Get the WABA ID from WhatsApp Manager > Account Tools > Phone Numbers
7. Get the Phone Number ID from the same page (click on the number)

Warning: connecting subscribes your own Meta app to this WABA with an override callback that redirects its webhook delivery to Zernio. This WABA's events stop reaching any callback URL you had configured before, immediately and with no overlap window. Do not unsubscribe your app from the WABA afterward: that also cuts off Zernio's delivery, and recovery requires calling this endpoint again.