woocommerce_package_rates not firing

Great plugin but the hook woocommerce_package_rate isn’t firing.

Currently trying to increase the outputted rate by x%, here is the following code:

Since the Echo on the console.log isn’t showing up, I’m assuming the woocommerce_package_rates isn’t firing. In that case, what would be the hook to use with flexible shipping?

add_filter('woocommerce_package_rates', 'add_percentage_to_shipping_cost', 10, 2);
function add_percentage_to_shipping_cost($rates, $package) {
    // I get the selected shipping method
    $chosen_shipping_method = WC()->session->get('chosen_shipping_methods')[0];
  echo '<script>console.log("Chosen Shipping Methods: ");</script>';

    // I've Defined the shipping method IDs for which I want to add 10%
    $target_shipping_methods = array(
        'flexible_shipping_ups:2:02', 
        'flexible_shipping_ups:2:03', 
        'flexible_shipping_ups:2:01', 
    );

  
    if (in_array($chosen_shipping_method, $target_shipping_methods)) {
        
        foreach ($rates as $rate_id => $rate) {
            
            if (in_array($rate_id, $target_shipping_methods)) {
               
                $new_cost = $rate->cost + ($rate->cost * 0.1);
                $rates[$rate_id]->cost = $new_cost;
            }
        }
    }

    return $rates;
}