<script async src="https://www.googletagmanager.com/gtag/js?id=UA-xxxxxxxx"></script> //Your Google Analytics ID
<script>
    window.dataLayer = window.dataLayer || [];
    function gtag(){ dataLayer.push(arguments); }
    gtag( 'js', new Date() );
    gtag( 'config', 'UA-xxxxxxxx-x' ); //Your Google Analytics ID
    gtag(
        'event', // Sends your conversion as an Event with the "ecommerce" "category" in your GA events reports
        'purchase', // Specifies the "action" of the event
        {
            'event_label': 'NAMEIT', // This is the "label" of the event. You can rename. (e.g. Plan2)
            'transaction_id': 'INVOICE NUMBER', // This is the ID of conversion. (e.g. 634)
            'value': XXX.00, // Specifies the total revenue or grand total associated with the transaction (e.g. 11.99)
            'currency': "XXX", // Local currency code. (e.g USD)
            'tax': 0.0, // Specifies the total shipping cost of the transaction. (e.g. 5)
            'shipping': 0, // Specifies the total tax of the transaction. (e.g. 1.29)
            "items": [
                {
                    "id": "Your Plan ID", // Transaction ID. For this specific case it's SKU. Required.
                    "name": "NameIt", // Product name. Required.
                    "quantity": XX, // Quantity. Required.
                    "price": "XX.0" // Price per Unit. Required.
                },
                {
                    "id": "Your Plan ID2",
                    "name": "NameIt2",
                    "quantity": XX,
                    "price": "XX.0"
                },
                {
                    "id": "Your Plan ID3",
                    "name": "NameIt3",
                    "quantity": XX,
                    "price": "XX.0"
                }
            ],
            'event_callback': function() {
                redirect(1000);
            }
        }
    );
</script>