Plugin development: get_post_meta is not working [closed]

I am trying to retrieve a post meta data using get_post_meta inside my plugin, but its not working.

add_action( 'woocommerce_checkout_update_order_meta', 'some_custom_checkout_field_update_order_meta',10,2);

function some_custom_checkout_field_update_order_meta( $order_id, $posted ) {

   global $woocommerce, $wpdb, $post ;

   //$user_custom_values = get_post_meta( $post->id, '_pallet-id', true);

   update_post_meta( $order_id, 'Pallet ID', $user_custom_values );

}