curl -X GET \
 /invoices/{invoiceId}/billing-run \
 --header "Authorization: Bearer <token>"

{
  "id": "<string>",
  "dateRangeFrom": "2023-11-07T05:31:56Z",
  "invoice": "https://example.com/",
  "subscriptions": [
    {
      "id": "ad8f1c2c-3b1c-4b0a-8b0a-0b0b0b0b0b0b",
      "externalId": "<string>",
      "number": "S-00000001",
      "name": "Fitness M",
      "billingGroup": {},
      "periods": [
        {
          "id": "<string>",
          "contractPeriodCount": 123,
          "contractPeriod": {},
          "cancellationPeriod": {}
        }
      ],
      "status": "active",
      "activatedAt": "2021-01-01T00:00:00+00:00",
      "poNumber": "PO-00000001",
      "contractDetails": {
        "contractStart": "2023-11-07T05:31:56Z",
        "contractEnd": "2023-11-07T05:31:56Z"
      },
      "trialEndsOn": "2021-01-01T00:00:00+00:00",
      "customFields": {
        "field1": "value1",
        "field2": "value2"
      },
      "nextBillingDate": "2023-11-07T05:31:56Z",
      "lastBillingAt": "2023-11-07T05:31:56Z",
      "partner": {
        "id": "ad8f7e7d-3b3b-4b3b-8b3b-3b3b3b3b3b3b",
        "name": "John Doe",
        "number": "123456",
        "email": "partner@example.com"
      }
    }
  ],
  "subscriptionItems": [
    {
      "id": "01F9ZQZJZJQZJZJZJZJZJZJZJZ",
      "name": "Fitness M",
      "description": "Everything included",
      "furtherInformation": "Additional agreements: The contract includes a free drink flatrate.",
      "status": "active",
      "subscriptionId": "<string>"
    }
  ],
  "billedAt": "2023-11-07T05:31:56Z",
  "dateRangeTo": "2023-11-07T05:31:56Z",
  "usageBreakdownUrl": "<string>"
}