Notification preferences

GET /portal/merchants/{merchant}/notifications (Owner/Admin) returns {version, events, daily_summary, email, phone, delivery}; before any change it is version 0 with nothing chosen. delivery reads NOT_CONFIGURED: no notification is sent.

POST …/notifications with an Idempotency-Key replaces the preferences at the version read: {expected_version, events, daily_summary, email, phone}. events has exactly PAYMENT_RECEIVED, PAYMENT_UNCERTAIN, REFUND_COMPLETED and SETTLEMENT_PAID, each {email, sms, whatsapp}; daily_summary is {email, whatsapp}, the summary the portal announces for 20:00 Kinshasa time; phone is +243 and nine digits. An email channel without an email returns 409 NOTIFICATION_EMAIL_REQUIRED, an SMS or WhatsApp channel without a number 409 NOTIFICATION_PHONE_REQUIRED, a stale version 409 NOTIFICATIONS_CHANGED. The email and number are stored encrypted. A retry under the same key with the same body answers with the preferences as they stand; another body under the key returns 409 IDEMPOTENCY_CONFLICT.