API: Invoice Email Delivery & Automatic Reminders

[0xdevcollins]

Summary

Implement invoice sending via email (Resend) and automatic payment reminders via BullMQ scheduled jobs.

Requirements

• POST /v1/invoices/:id/send — Send invoice to customer via email
  • Custom message field in request body
  • Email includes: merchant branding, invoice summary, "Pay Now" CTA button linking to checkout
  • Update status to SENT
• Track when customer views invoice email (pixel/link tracking) → update to VIEWED
• Automatic reminders via BullMQ:
  • 3 days before due date
  • On due date
  • 3 days after due date (mark as OVERDUE)
• Reminder emails use Resend templates with merchant branding

Dependencies

• Notifications module (Resend) — already implemented
• BullMQ — already configured

Acceptance Criteria

• Invoice sent via email with merchant branding and pay link
• View tracking updates invoice status
• 3 reminder jobs scheduled automatically on invoice send
• Overdue status applied automatically after due date + 3 days
• Webhook events fired: invoice.sent, invoice.viewed, invoice.overdue