Snippet to auto choose the shipping method on creating the UPS label, even the order is placed non-ups services. Work with pluginhive UPS shipping https://www.pluginhive.com/product/woocommerce-ups-shipping-plugin-with-print-label/

gistfile1.txt

add_filter('ph_ups_label_shipping_method', 'ph_ups_label_shipping_method', 10, 2);
function ph_ups_label_shipping_method( $shippingmethod, $order ){

	//Config this array
	$shipping_method_map = array(
		'free_shipping' => '03',
		'flat_rate'		=> '12',
	);


	$shipping_method = @array_shift($order->get_shipping_methods());
	$shipping_method_id = $shipping_method['method_id'];

	return isset( $shipping_method_map[$shipping_method_id] ) ? $shipping_method_map[$shipping_method_id] : $shippingmethod;
}