curl --request POST \
  --url https://api.fint.app/api/v1/invoice \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '
{
  "date": "<string>",
  "expirationDate": "<string>",
  "contactId": 123,
  "description": "<string>",
  "totalAmount": 123,
  "externalReference": "<string>",
  "sendEmail": true,
  "items": [
    {
      "itemId": 123,
      "quantity": 1
    }
  ],
  "itemGroups": [
    {
      "itemGroupId": 123,
      "selectedItems": [
        {
          "itemId": 123,
          "quantity": 1
        }
      ]
    }
  ],
  "customItems": [
    {
      "name": "<string>",
      "amount": 123,
      "quantity": 123,
      "description": "<string>",
      "details": {
        "discountItemId": 123,
        "amountType": "<string>",
        "configuredAmount": 123,
        "condition": "<string>",
        "conditionItems": [
          {
            "id": 123
          }
        ],
        "baseAmount": 123,
        "appliedAmount": 123,
        "maxDiscountAmount": 123,
        "cartItems": [
          {
            "itemId": 123,
            "totalAmount": 123
          }
        ],
        "breakdown": [
          {
            "itemId": 123,
            "discountAmount": 123
          }
        ]
      }
    }
  ]
}
'

{
  "invoiceId": 123,
  "contactId": 123
}