POST "https://api.rewards.wlloyalty.net/events"
  Content-Type: "application/json"
  X-Api-Key: foobar123
  Authorization: Bearer ...

  {
    "type": "INVOICE_PAID",
    "subject": "431a81d8-3936-4ccc-8955-2009c078e6c8",
    "payload": {
      "invoiceId": "031a81d8-2936-4ccc-8955-3009c078e6f1",
      "balance": 0,
      "overdue": true,
      "daysLate": 4,
      "paymentMethod": "CASH"
    }
  }