GooglePay.js

$.when(adrma.fetchData({
        url: "https://pay.google.com/gp/p/js/pay.js",
        dataType: "script",
    }),

    adrma.fetchData({
        url: "https://js.braintreegateway.com/web/3.64.1/js/client.min.js",
        dataType: "script",
    }),

    adrma.fetchData({
        url: "https://js.braintreegateway.com/web/3.64.1/js/google-payment.min.js",
        dataType: "script",
})).then(function() {    

    // You will need a button element on your page styled according to Google's brand guidelines
    // https://developers.google.com/pay/api/web/guides/brand-guidelines

    var paymentsClient = new google.payments.api.PaymentsClient({
        environment: 'TEST' // Or 'PRODUCTION'
    });

    braintree.client.create({
        authorization: "sandbox_ykvt3vxx_hcrc97h9tfbz8b6c"
    }, function(clientErr, clientInstance) {
        braintree.googlePayment.create({
            client: clientInstance,
            googlePayVersion: 2,
            googleMerchantId: 'BCR2DN6T3PSN74SE' // Optional in sandbox; if set in sandbox, this value must be a valid production Google Merchant ID
        }, function(googlePaymentErr, googlePaymentInstance) {
            paymentsClient.isReadyToPay({
                // see https://developers.google.com/pay/api/web/reference/object#IsReadyToPayRequest
                apiVersion: 2,
                apiVersionMinor: 0,
                allowedPaymentMethods: googlePaymentInstance.createPaymentDataRequest().allowedPaymentMethods,
                existingPaymentMethodRequired: true // Optional
            }).then(function(response) {
                if (response.result) {

                    var gPaybutton = paymentsClient.createButton({
                        onClick: (event) => {
                            event.preventDefault();

                            var paymentDataRequest = googlePaymentInstance.createPaymentDataRequest({
                                transactionInfo: {
                                    currencyCode: 'USD',
                                    totalPriceStatus: 'FINAL',
                                    totalPrice: '100.00' // Your amount
                                }
                            });
    
                            // We recommend collecting billing address information, at minimum
                            // billing postal code, and passing that billing postal code with all
                            // Google Pay card transactions as a best practice.
                            // See all available options at https://developers.google.com/pay/api/web/reference/object
                            var cardPaymentMethod = paymentDataRequest.allowedPaymentMethods[0];
                            cardPaymentMethod.parameters.billingAddressRequired = true;
                            cardPaymentMethod.parameters.billingAddressParameters = {
                                format: 'FULL',
                                phoneNumberRequired: true
                            };
    
                            paymentsClient.loadPaymentData(paymentDataRequest).then(function(paymentData) {
                                googlePaymentInstance.parseResponse(paymentData, function(err, result) {
                                    if (err) {
                                        // Handle parsing error
                                    }
    
                                    // Send result.nonce to your server
                                    // result.type may be either "AndroidPayCard" or "PayPalAccount", and
                                    // paymentData will contain the billingAddress for card payments
                                });
                            }).catch(function(err) {
                                // Handle errors
                            });
                        }
                    });

                    $(".purchase-cta-secondary").prepend(gPaybutton);                                     
                }
            }).catch(function(err) {
                // Handle errors
            });
        });

        // Set up other Braintree components
    });

});