I have the following JSON string, i try to decode with php json_decode but $postarray is always NULL, can't work out why this is?

Running on Debian 5.0 Linux php Client API version => 5.0.51a Json version 1.2.1

 $json = '{\"json\":[{\"username\":\"1062576\",\"accountId\":\"45656565\"}]}';

 $postarray = json_decode($json);
 print_r($postarray);

Teşekkürler