List one-time bill items

curl --request GET \
  --url https://api.helloproper.com/one-time-bill-items \
  --header 'Authorization: <api-key>'

{
  "oneTimeBillItems": [
    {
      "id": "<string>",
      "leaseId": "<string>",
      "created": "<string>",
      "modified": "<string>",
      "productKey": "<string>",
      "description": "<string>",
      "amount": {
        "currency": "<string>",
        "amount": 123
      },
      "quantity": 123,
      "unitNetPrice": {
        "currency": "<string>",
        "amount": 123
      },
      "netPrice": {
        "currency": "<string>",
        "amount": 123
      },
      "dueDate": "<string>",
      "accountingPeriod": "<string>",
      "vat": {
        "taxMode": "<string>",
        "taxRate": 123
      }
    }
  ]
}