curl --request POST \
  --url https://api.hel.io/v1/transaction/headless/prepare \
  --header 'Content-Type: application/json' \
  --data '
{
  "paymentRequestId": "<string>",
  "senderPublicKey": "<string>",
  "currencyId": "<string>",
  "quantity": 123,
  "minimalUnitAmount": 123,
  "affiliateCode": "<string>",
  "btcPublicKey": "<string>",
  "customerDetails": {
    "email": "<string>",
    "discordUser": {
      "id": "<string>",
      "username": "<string>"
    },
    "twitterUsername": "<string>",
    "telegramUser": {
      "id": 123,
      "username": "<string>"
    },
    "fullName": "<string>",
    "country": "<string>",
    "state": "<string>",
    "city": "<string>",
    "street": "<string>",
    "streetNumber": "<string>",
    "areaCode": "<string>",
    "deliveryAddress": "<string>",
    "blinkAddress": "<string>",
    "phoneNumber": "<string>",
    "additionalJSON": "<string>",
    "btcProperties": {
      "ordinalsAddress": "<string>"
    }
  },
  "productDetails": {
    "name": "<string>",
    "value": "<string>",
    "active": true
  }
}
'

{
  "transactionToken": "string",
  "transactionMessage": "string",
  "serializedTransaction": "string",
  "addressLookupTableAccounts": [
    "string"
  ]
}