Flutter でGoogle Pay の実装

{
  "provider": "google_pay",
  "data": {
    "environment": "TEST",
    "apiVersion": 2,
    "apiVersionMinor": 0,
    "allowedPaymentMethods": [
      {
        "type": "CARD",
        "tokenizationSpecification": {
          "type": "PAYMENT_GATEWAY",
          "parameters": {
            "gateway": "example",
            "gatewayMerchantId": "gatewayMerchantId"
          }
        },
        "parameters": {
          "allowedCardNetworks": [
            "VISA",
            "MASTERCARD",
            "JCB",
            "AMEX"
          ],
          "allowedAuthMethods": [
            "PAN_ONLY",
            "CRYPTOGRAM_3DS"
          ]
        }
      }
    ],
    "merchantInfo": {
      "merchantId": "01234567890123456789",
      "merchantName": "service name"
    },
    "transactionInfo": {
      "countryCode": "JP",
      "currencyCode": "JPY"
    }
  }
}