curl --request POST \
  --url https://api.helloproper.com/recurring-bill-items \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '{
  "leaseId": "<string>",
  "recurringBillItem": {
    "productKey": "<string>",
    "description": "<string>",
    "amount": {
      "currency": "<string>",
      "amount": 123
    },
    "quantity": 123,
    "vat": {
      "taxMode": "<string>",
      "taxRate": 123
    },
    "dueDateRule": {
      "dayOfPeriod": 123
    },
    "billingCycle": {
      "timeUnit": "<string>",
      "periodLength": 123,
      "start": 123
    },
    "startedOn": "<string>",
    "firstBillingPeriodBillItem": {
      "amount": {
        "currency": "<string>",
        "amount": 123
      },
      "dueDate": "<string>",
      "accountingPeriod": "<string>"
    },
    "discount": {
      "amount": {
        "currency": "<string>",
        "amount": 123
      },
      "percentage": 123,
      "description": "<string>",
      "endDate": "<string>"
    }
  }
}'

{
  "recurringBillItemId": "<string>",
  "firstDueDate": "<string>"
}