How to add pay now button for making payment in the My account invoice.

• Created a new extension as invoice pay now button and extend the view and template . 
•   Added the button in the template and created the pay now button. 

•  Stored the link in a variable and passed the link to the button. 

• Made the invoice ID dynamic by getting the invoice id and stored in variable and passed the variable in link  
   
• So when we click the link page will navigate to payment page 

Extension:
define(
    'JJ.invoice_paynow_button.Invoicepaynowbutton', ['Invoice.Details.View', 'jj_invoice_paynow_button_invoicepaynowbutton.tpl'],
    function(InvoiceDetailsView, jj_invoice_paynow_button_invoicepaynowbutton_tpl, ) {
        'use strict';

        return {
            mountToApp: function mountToApp(container) {
                // using the 'Layout' component we add a new child view inside the 'Header' existing view 
                // (there will be a DOM element with the HTML attribute data-view="Header.Logo")
                // more documentation of the Extensibility API in
                // https://system.netsuite.com/help/helpcenter/en_US/APIs/SuiteCommerce/Extensibility/Frontend/index.html

                /** @type {LayoutComponent} */
                var layout = container.getComponent('Layout');

                _.extend(InvoiceDetailsView.prototype, {
                    template: jj_invoice_paynow_button_invoicepaynowbutton_tpl,

                    getContext: _.wrap(InvoiceDetailsView.prototype.getContext, function(fn) {
                        var context = fn.apply(this, _.toArray(arguments).slice(1));
                        var internal_id = this.model.internalid
                        var paynow = 'https://checkout.paystand.co/v4/?publishableKey=jevmz9mey2njn2et5ewqvl9z&viewCheckout=portal-medium&module=ns_invoice&extInvoiceId=' + internal_id + '&externalCss=https:%2F%2F3425005-sb1.app.netsuite.com%2Fcore%2Fmedia%2Fmedia.nl%3Fid%3D35337581%26c%3D3425005_SB1%26h%3DaNyoyCA44ZlNLuC0s8-eqWE5xOW5Uw5qQ-6qUZdhXS3Zgv_E%26_xt%3D.css&logoUrl=https:%2F%2F3425005-sb1.app.netsuite.com%2Fcore%2Fmedia%2Fmedia.nl%3Fid%3D35337580%26c%3D3425005_SB1%26h%3D_B420yQ0SisY2CLGy4rmKE8H1bs5fIlamBIId_ViW6A7Q2Ws%0A&drawerType=open ';

                        context.internal_id = internal_id;


                        context.paynow = paynow;
                        return context;
                    })
                });


            }
        };
    });