Change SKU argument to Product ID

add_filter('pr_shipping_dhl_label_args', 'modify_item_sku', 10, 2);
function modify_item_sku($args, $order_id) {
	if( isset( $args['items'] ) ) {
		foreach ($args['items'] as $item_key => $item_value) {
			if( isset( $item_value['sku'] ) ) {
				$product_id = wc_get_product_id_by_sku( $item_value['sku'] );
				if( $product_id ) {
					$args['items'][ $item_key ]['sku'] = $product_id;
				}
			}
		}
	}
	return $args;
}