Ошибка: cannot use string offset as an array...

    function curl($url) {
        $ch = curl_init($url);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
        $response = curl_exec($ch);
        curl_close($ch);
        return $response;
    }
    
    function api($method) {
        $response = curl("https://api.vk.com/method/".$method);
        $json = json_decode($response, true);
        if($json["error"]["error_msg"]) {
            return $json["error"];
        } else {
            return $json["response"];
        }
    }

if($json["error"]["error_msg"]) {

var_dump($json);

function by($method) {
    $response = curl("https://api.vk.com/method/".$method);
    $json = json_decode($response, true);
    var_dump($json);
    if(($json["error"]["error_msg"])) {
        return $json["error"];
    } else {
        return $json["response"];
    }
}

if(array_key_exists('error', $json)) {
        return $json["error"];
    } else {
        return $json["response"];
    }

$wall_get = api ('wall.getComments?owner_id='.$wall_id."&post_id=".$post_id."&sort=desc&count=1&access_token=".$token);
$uid = $wall_get[1]["uid"];
$cid = $wall_get[1]["cid"];
$wall_text = $wall_get[1]["text"];
 
if (preg_match('/Помощь/i', $wall_text)) {
    $text = random (array('Что','Какие команды','Ты о чем'));
    echo $text;
}elseif (preg_match('/Привет/i', $wall_text)) {
    $text = 'Привет';
}elseif(preg_match('/Как дела/i', $wall_text)) {
    $text = ("да ну *****");
 
}
 
if ($id_bot == $uid) {
    echo ("$time No Otvet\n");
    die;
}  
 
$commet = api("wall.createComment?owner_id=".$wall_id."&post_id=".$post_id."&reply_to_comment=".$cid."&message=".$text."&from_group=0&access_token=".$token);
 
Print_r ($commet);  
function api($method) {
    $response = curl("https://api.vk.com/method/" . $method);
    $json = json_decode($response, true);
    if( !empty($json["response"]) ) {
        return $json["response"];
    } else {
        return $json["error"];
    }
}
 
function random($text){
$rand = mt_rand (0, count($text)-1); 
return $text[$rand]; 
}
 
function curl( $url ){
$ch = curl_init( $url );
curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
curl_setopt( $ch, CURLOPT_SSL_VERIFYHOST, false );
curl_setopt( $ch, CURLOPT_SSL_VERIFYPEER, false );
$response = curl_exec( $ch );
curl_close( $ch );
return $response;
}

var_dump($json)