Ldap PHP / Stronger authentication

PHP Version: 5.6.

I would like to ask you for help in the case of LDAP authentication - PHP.

I have got script:

if(isset($_POST['username']) && isset($_POST['password'])){

$adServer = "ldaps://###";

$ldap = ldap_connect($adServer);
$username = $_POST['username'];
$password = $_POST['password'];

$ldaprdn = 'AD' . "\\" . $username;

ldap_set_option($ldap, LDAP_OPT_PROTOCOL_VERSION, 3);
ldap_set_option($ldap, LDAP_OPT_REFERRALS, 0);

$bind = ldap_bind($ldap, $ldaprdn, $password);

if ($bind) {

} else {
    $msg = "Invalid email address / password";
    echo $msg."</br>".$ldaprdn."</br>";

The issue is I'm always receiving

Warning: ldap_bind(): Unable to bind to server: Strong(er) authentication required

I'm using in $adServer - ldapS. I also uncommented the line 'openssl' in php.ini. IIS has been restarted, but still this same issue.

I tried also read some articles here but nothing happened. Just know that the authentication works good, but it need stronger auth.

Should I add any new Certificate to host? Should I try any port? 636?

In case of any questions do not hesitate to write here. Thank you