Add Custom Fields to WooCommerce Checkout and Store in Order Details Page

file.php

add_action('woocommerce_after_order_notes', 'my_custom_checkout_field');

function my_custom_checkout_field( $checkout ) {
	
	echo '<div id="my_custom_checkout_field"><h3>'.__('My Field').'</h3>';
				
	woocommerce_form_field( 'my_field_name', array( 
		'type' 			=> 'text', 
		'class' 		=> array('my-field-class orm-row-wide'), 
		'label' 		=> __('Fill in this field'),
		'required'		=> true,
		'placeholder' 	=> __('Enter a number'),
		), $checkout->get_value( 'my_field_name' ));

	echo '</div>';
}

/**
 * Process the checkout
 **/
add_action('woocommerce_checkout_process', 'my_custom_checkout_field_process');

function my_custom_checkout_field_process() {
	global $woocommerce;
	
	if ( ! $_POST['my_field_name'] )
        wc_add_notice( __( 'Please fill My Field.' ), 'error' );
}

/**
 * Update the user meta with field value
 **/
add_action('woocommerce_checkout_update_user_meta', 'my_custom_checkout_field_update_user_meta');

function my_custom_checkout_field_update_user_meta( $user_id ) {
	if ($user_id && $_POST['my_field_name']) update_user_meta( $user_id, 'my_field_name', esc_attr($_POST['my_field_name']) );
}

/**
 * Update the order meta with field value
 **/
add_action('woocommerce_checkout_update_order_meta', 'my_custom_checkout_field_update_order_meta');

function my_custom_checkout_field_update_order_meta( $order_id ) {
	if ($_POST['my_field_name']) update_post_meta( $order_id, 'My Field', esc_attr($_POST['my_field_name']));
}

/**
 * Add the field to order emails

add_filter('woocommerce_email_order_meta_keys', 'my_custom_checkout_field_order_meta_keys');

function my_custom_checkout_field_order_meta_keys( $keys ) {
	$keys[] = 'My Field';
	return $keys;
} **/

It is working. Thanks!