curl --request POST \
  --url https://api.steppay.kr/api/v1/invoices \
  --header 'Content-Type: application/json' \
  --header 'Secret-Token: <api-key>' \
  --data '
{
  "customerId": 1,
  "items": [
    {
      "productCode": "<string>",
      "priceCode": "<string>",
      "minimumQuantity": 123,
      "maximumQuantity": 123,
      "productName": "<string>",
      "price": 123
    }
  ],
  "publishType": "NOW",
  "publishMethods": [],
  "invoicePayMethods": [],
  "discount": 0,
  "purchaseDeadline": "2023-11-07T05:31:56Z",
  "reservationAt": "2023-11-07T05:31:56Z",
  "instantAmount": 1,
  "memoToCustomer": "<string>",
  "currency": "<string>"
}
'

{
  "id": 123
}