Online PHP editor | output for rCVEB

<?php $a = Array ( 'meta' => Array ( 'code' => 200, 'type' => 'Success', 'message' => 'Success' ), 'data' => Array ( 'items' => Array ( '0' => Array ( 'id' => 'b4a235596fd9550dfb69f181f4db007f', 'tracking_number' => 2649884668232181, 'carrier_code' => 'hermes', 'order_create_time' => '', 'destination_code' => '', 'status' => 'delivered', 'track_update' => '', 'original_country' => '', 'itemTimeLength' => 7, 'stayTimeLength' => 74, 'service_code' => '', 'packageStatus' => '', 'substatus' => '', 'last_mile_tracking_supported' => '', 'origin_info' => Array ( 'ItemReceived' => '2019-04-09 09:29', 'ItemDispatched' => '', 'DepartfromAirport' => '', 'ArrivalfromAbroad' => '', 'CustomsClearance' => '', 'DestinationArrived' => '', 'weblink' => 'https://www.hermesworld.com/en/', 'phone' => '', 'carrier_code' => 'hermes', 'trackinfo' => Array ( '0' => Array ( 'Date' => '2019-04-15 11:51', 'StatusDescription' => 'Posted through letterbox', 'Details' => '', 'checkpoint_status' => 'delivered' ), '1' => Array ( 'Date' => '2019-04-15 09:45', 'StatusDescription' => 'Delivery will be attempted between 10:00 and 14:00 today ', 'Details' => '', 'checkpoint_status' => 'transit' ), '2' => Array ( 'Date' => '2019-04-15 06:39', 'StatusDescription' => 'On its way to the courier', 'Details' => '', 'checkpoint_status' => 'transit' ), '3' => Array ( 'Date' => '2019-04-14 22:33', 'StatusDescription' => 'At the customers local depot', 'Details' => '', 'checkpoint_status' => 'transit ' ) ) ), 'destination_info' => '', 'lastEvent' => 'Posted through letterbox,2019-04-15 11:51', 'lastUpdateTime' => '2019-04-15 11:51' ) ) ) ); $r = []; array_walk_recursive($a, function($v, $k) use(&$r){ ($k == 'checkpoint_status') ? ($r[]=$v) : ''; }); print_r($r);