WooCommerce: Send a second email to customer if a coupon is applied with HTML

woo_sent_coupon_mail.php

// In theme's functions.php or plug-in code:

// wp_mail() sents emails only in plain text by default, here we add HTML support
function wp_set_content_type(){
    return "text/html";
}
add_filter( 'wp_mail_content_type','wp_set_content_type' );

function action_woocommerce_applied_coupon( $coupon_code ) {
    // NOT logged in, return
    if ( ! is_user_logged_in() ) return;
    
    // Compare
    if ( $coupon_code == 'freeclass' ) {
        // Get user ID
        $user_id = get_current_user_id();
        
        // Get the WC_Customer instance Object
        $customer = New WC_Customer( $user_id );
        
        // Billing email
        $email = $customer->get_billing_email();

        // NOT empty
        if ( ! empty ( $email ) ) {
            // Recipient
            $to = $email;
            $subject = sprintf( __('Coupon "%s" has been applied', 'woocommerce' ), $coupon_code );
            $content = sprintf( __('The coupon code "%s" has been applied', 'woocommerce' ), $coupon_code );

            wp_mail( $to, $subject, $content );
        }
    }
}
add_action( 'woocommerce_applied_coupon', 'action_woocommerce_applied_coupon', 10, 1 );