Custom Input Field For COD

<?php
/**
 * Output a single payment method
 *
 * This template can be overridden by copying it to yourtheme/woocommerce/checkout/payment-method.php.
 *
 * HOWEVER, on occasion WooCommerce will need to update template files and you
 * (the theme developer) will need to copy the new files to your theme to
 * maintain compatibility. We try to do this as little as possible, but it does
 * happen. When this occurs the version of the template file will be bumped and
 * the readme will list any important changes.
 *
 * @see         https://docs.woocommerce.com/document/template-structure/
 * @package     WooCommerce/Templates
 * @version     3.5.0
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}
?>
<li class="wc_payment_method payment_method_<?php echo esc_attr( $gateway->id ); ?>">
    <input id="payment_method_<?php echo esc_attr( $gateway->id ); ?>" type="radio" class="input-radio" name="payment_method" value="<?php echo esc_attr( $gateway->id ); ?>" <?php checked( $gateway->chosen, true ); ?> data-order_button_text="<?php echo esc_attr( $gateway->order_button_text ); ?>" />

     <label for="payment_method_<?php echo esc_attr( $gateway->id ); ?>">
        <?php echo $gateway->get_title(); /* phpcs:ignore WordPress.XSS.EscapeOutput.OutputNotEscaped */ ?> <?php echo $gateway->get_icon(); /* phpcs:ignore WordPress.XSS.EscapeOutput.OutputNotEscaped */ ?>
    </label>
    <?php  if ( $gateway->has_fields()  || $gateway->get_description()  ) : ?>
        <div class="payment_box payment_method_<?php echo esc_attr( $gateway->id ); ?>" <?php if ( ! $gateway->chosen ) : /* phpcs:ignore Squiz.ControlStructures.ControlSignature.NewlineAfterOpenBrace */ ?>style="display:none;"<?php endif; /* phpcs:ignore Squiz.ControlStructures.ControlSignature.NewlineAfterOpenBrace */ ?>>


/////// HERE IS THE CUSTOM INPUT FIELD WHICH displays A INPUT FIELD WHEN COD IS SELECTED


    <?php if ( $gateway->has_fields() || /* $gateway->get_description() && */ $gateway->id != "cod" ) : ?>
<?php endif; ?>
<?php if ( $gateway->id == "cod" ) : ?>
<div class="payment_box payment_method_<?php echo $gateway->id; ?>" <?php if ( ! $gateway->chosen ) : ?>style="display:none;"<?php endif; ?>>
    <input type="text" name='cod_custom_field' placeholder="Enter Your Margin" >
            </div>
<?php endif; ?>



            <?php $gateway->payment_fields(); ?>
        </div>
    <?php endif; ?>
</li>