如何修复JSON_ERROR_UTF8

Question

I want to get JSON but it is not working when there is a "Ñ". I have a change the collation of my database to utf8_general_ci. The total count of the data is 2292. When I use json_encode nothing appears but when I use echo the data appears. How can I fix this?

$sql = "SELECT FileAs FROM tblContacts WHERE Coordinator = '$ContactID'";
$result = mysqli_query($conn, $sql);
$count = mysqli_num_rows($result);

if($count > 0){
   while ($row = mysqli_fetch_array($result)) {
       $ar[] = array(
           'FileAs' => $row['FileAs']
       );
    }
} 

print json_encode($ar);