tokenizationSpecification for UPI, and there gatewayMerchantId

i wants to add payment with gpay without any others payment getway, if it is posible the please help me out. i using below code just for testing perpose.

{
  "provider": "google_pay",
  "data": {
    "environment": "TEST",
    "apiVersion": 2,
    "apiVersionMinor": 0,
    "allowedPaymentMethods": [
      {
        "type": "CARD",
        "tokenizationSpecification": {
          "type": "PAYMENT_GATEWAY",
          "parameters": {
            "gateway": "example",
            "gatewayMerchantId": "123456789890"
          }
        },
        "parameters": {
          "allowedCardNetworks": ["VISA", "MASTERCARD"],
          "allowedAuthMethods": ["PAN_ONLY", "CRYPTOGRAM_3DS"],
          "billingAddressRequired": true,
          "billingAddressParameters": {
            "format": "FULL",
            "phoneNumberRequired": true
          }
        }
      }
    ],
    "merchantInfo": {
      "merchantId": "12345678906789",
      "merchantName": "Developer_test"
    },
    "transactionInfo": {
      "countryCode": "US",
      "currencyCode": "USD"
    }
  }
}

Thank you.