Загрузка фотографий - vk-api

Есть код:

$hash = '550fa6d13e5481a5049b8df2d0fec132';
$photo = '[{"photo":"a060d15ff5:y","sizes":[["s","639420229","3f6e3","-h4FeOcwms8",75,57],["m","639420229","3f6e4","SrWCWTzpO9s",130,99],["x","639420229","3f6e5","r9nc-PBAuVw",604,460],["y","639420229","3f6e6","BMoQlkfUIAA",775,590],["o","639420229","3f6e7","mGhryO7f6j4",130,99],["p","639420229","3f6e8","dvgIdscufxY",200,152],["q","639420229","3f6e9","JSTfcgtNJaA",320,244],["r","639420229","3f6ea","YLTaHbyu2ZM",510,388]],"kid":"7fbc1b8649663696ba48164aa7216248","debug":"xsymyxyyyoypyqyry","peer_id":344029086}]';
$server = '639420';
$safe = file_get_contents("https://api.vk.com/method/photos.saveMessagesPhoto?server=".$server."&photos_list=".$photo."&hash=".$hash."&access_token=".$token);
$safe = json_decode($safe,true);

В ответ возвращает, что неверно подана картинка:

[error] => Array
    (
        [error_code] => 100
        [error_msg] => One of the parameters specified was missing or invalid: photo is undefined
        [request_params] => Array
            (
                [0] => Array
                    (
                        [key] => oauth
                        [value] => 1
                    )
                [1] => Array
                    (
                        [key] => method
                        [value] => photos.saveMessagesPhoto
                    )
                [2] => Array
                    (
                        [key] => server
                        [value] => 639420
                    )
                [3] => Array
                    (
                        [key] => photos_list
                        [value] => [{"photo":"a060d15ff5:y","sizes":[["s","639420229","3f6e3","-h4FeOcwms8",75,57],["m","639420229","3f6e4","SrWCWTzpO9s",130,99],["x","639420229","3f6e5","r9nc-PBAuVw",604,460],["y","639420229","3f6e6","BMoQlkfUIAA",775,590],["o","639420229","3f6e7","mGhryO7f6j4",130,99],["p","639420229","3f6e8","dvgIdscufxY",200,152],["q","639420229","3f6e9","JSTfcgtNJaA",320,244],["r","639420229","3f6ea","YLTaHbyu2ZM",510,388]],"kid":"7fbc1b8649663696ba48164aa7216248","debug":"xsymyxyyyoypyqyry","peer_id":344029086}]
                    )
                [4] => Array
                    (
                        [key] => hash
                        [value] => 550fa6d13e5481a5049b8df2d0fec132
                    )
            )
    )

Что именно не так?