Calculating Percentage of Total Cart Price with Shipping Fee

Hi, I customized the checkout page by adding a 3.5% percentage fee for Paymongo Credit Card payment gateway.

However with my code now, it’s only calculating 3.5% of the cart total EXCLUDING shipping fee. How can I alter the code below that calculates it WITH the shipping fee? Thank you so much!

// Adding fee for Paymongo

add_action( 'woocommerce_cart_calculate_fees','ts_add_discount', 20, 1 );

function ts_add_discount( $cart_object ) {

if ( is_admin() && ! defined( 'DOING_AJAX' ) ) return;

// Mention the payment method e.g. cod, bacs, cheque or paypal
$payment_method = 'paymongo';

// The percentage to apply
$percent = 3.5; // 3.5%

$cart_total = $cart_object->subtotal_ex_tax;

$chosen_payment_method = WC()->session->get('chosen_payment_method'); //Get the selected payment method

if( $payment_method == $chosen_payment_method ){

$label_text = __( "PayMongo Convenience Fee (3.5%)" );

// Calculating percentage
$discount = number_format(($cart_total / 100) * $percent, 3.5);

// Adding the discount
$cart_object->add_fee( $label_text, +$discount, false );
}
}

add_action( 'woocommerce_review_order_before_payment', 'ts_refresh_payment_method' );

function ts_refresh_payment_method(){
// jQuery
?>
<script type="text/javascript">
(function($){
$( 'form.checkout' ).on( 'change', 'input[name^="payment_method"]', function() {
$('body').trigger('update_checkout');
});
})(jQuery);
</script>
<?php
}

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