WHATSAPP PAYMENT CONFIRMATION (Cloud API)
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1) Meta Developers -> WhatsApp -> Cloud API:
   - Connect your WhatsApp Business Account + Phone Number
   - Get: Phone Number ID + Permanent Access Token
2) Create & approve templates (business initiated):
   - sendzim_payment_confirmed (params: amount, currency, receiver_name, method, ref)
   - sendzim_transfer_created  (params: amount, currency, method, ref)
3) Edit backend/config/config.php:
   - set whatsapp.enabled = true
   - set access_token, phone_number_id
   - set admin_notify_number (optional)

Reminder: WhatsApp requires user opt-in. Use templates for business-initiated notifications.
