1. Create the Google Pay UI button according to the instructions in the Google Pay for Web Payments Brand Guidelines Guide.
  2. On your payment page, define the tokenizationSpecification constant as shown below.
    (When the customer presses the Google Pay button, this parameter identifies your gateway and your site’s gateway merchant identifier.)
    Example tokenizationSpecification Constant in an /initPayment Request
    const tokenizationSpecification = {
  type: "PAYMENT_GATEWAY",
  parameters: {
    "gateway": "nuveidigital",
    "gatewayMerchantId": "googletest", //'googletest' for test or 'nuveidigital' for production
  }
};