Add Custom Fields to Shipping Method

// Add custom fields to a specific selected shipping method
add_action( 'woocommerce_after_shipping_rate', 'carrier_custom_fields', 20, 2 );
function carrier_custom_fields( $method, $index ) {
   
  if( ! is_checkout()) return; // Only on checkout page
    //change this to the shipping method you are adding the custom field to
    $customer_carrier_method = 'local_pickup:1';

    if( $method->id != $customer_carrier_method ) return; 
      //get the selected shipping method
      $chosen_method_id = WC()->session->chosen_shipping_methods[ $index ];

      if($chosen_method_id == $customer_carrier_method ):
        echo '<div class="custom-carrier">';
        
        //create custom field 
        woocommerce_form_field( 'carrier_number' , array(
          'type'          => 'text',
          'class'         => array('form-row-wide carrier-number'),
          'required'      => true,
          'placeholder'   => 'FedEx Account Number',
        ), WC()->checkout->get_value( 'carrier_number' ));
  
        echo '</div>';
      endif;
}

// Check custom fields validation
add_action('woocommerce_checkout_process', 'carrier_checkout_process');
function carrier_checkout_process() {
    if( isset( $_POST['carrier_number'] ) && empty( $_POST['carrier_number'] ) )
        wc_add_notice( ( "Specify your FedEx account number." ), "error" );
}

// Save custom fields to order meta data
add_action( 'woocommerce_checkout_update_order_meta', 'carrier_update_order_meta', 30, 1 );
function carrier_update_order_meta( $order_id ) {

    if( isset( $_POST['carrier_number'] ))
        update_post_meta( $order_id, '_carrier_number', sanitize_text_field( $_POST['carrier_number'] ) );
}

// Add Customer FedEx Account Number to admin order data
add_action( 'woocommerce_admin_order_data_after_shipping_address', 'misha_editable_order_meta_shipping' );

function misha_editable_order_meta_shipping( $order ){

	$carrier_number = get_post_meta( $order->get_id(), '_carrier_number', true );
		
	?>
	<div class="address">
		<p<?php if( empty($carrier_number) ) echo ' class="none_set"' ?>>
 			<strong>Customer FedEx Account Number:</strong>
			<?php echo ( !empty( $carrier_number ) ) ? $carrier_number : 'Not specified' ?>
		</p>
	</div>
	<div class="edit_address"><?php
		woocommerce_wp_text_input( array( 
			'id' => 'carrier_number',
			'label' => 'Customer FedEx Account Number', 
			'wrapper_class' => 'form-field-wide',
			'class' => 'form-field form-field-wide carrier-number',
			'style' => 'width:100%; padding: 0 8px',
			'value' => $carrier_number,
			'description' => 'This is the customer supplied FedEx account number to use for shipping.'
		) );
	?></div><?php
}

add_action( 'woocommerce_process_shop_order_meta', 'misha_save_shipping_details' );
function misha_save_shipping_details( $ord_id ){
	update_post_meta( $ord_id, '_carrier_number', wc_clean( $_POST[ 'carrier_number' ] ) );
}