这是什么意思?->警告:非法字符串偏移量[重复]

thread

Warning: Illegal string offset 'admin_db' in C:\wamp64\www\NewKali\includes\user.inc.php on line 55

public function isAdmin($user){
    $userToGet = $user;

    $stmt = $this->Connect()->prepare("SELECT admin_db FROM user_secure WHERE username_db=?");
    $query1 = $stmt->execute([$userToGet]);

    if(!$query1)
    {
      die("Execute query error, because: ". print_r($this->Connect()->errorInfo(),true) );
    }else{
        foreach ( $stmt->fetch() as $row) {
            $value = $row["admin_db"];
                 if($value == 1){
                    return true;
                 } else {
                    return false;
                 }
             }
    }
}