Login error with hash password using PHP, mysql and PDO for accessing database.

Parse error: syntax error, unexpected '{'

<?php
    $sql = "SELECT * FROM tbl_user WHERE username = ?";
    $stmt = $db->prepare($sql);
    $result = $stmt->execute([$_POST['username']]);
    $un = $result->fetchAll();
        if (isset($un[0]) {
        if (password_verify($_POST['password'], $un[0]->password) {
            echo "login success";
          } else {
            echo "wrong password";
          }
        } 
?>