Unable to checkout in wordpress due to error “hook uses out of date data structures

Solution:

In WC version 3.0.0 we use woocommerce_add_order_item_meta hook and add item meta like this

wc_add_order_item_meta ( $item_id, $key, $value );

But from WC version 3.0.0+ we have to use this hook woocommerce_checkout_create_order_line_item and add order item meta like this

$item->add_meta_data($key,$order_val);