LDAPs Query from Active directory - php

Question

The goal is to connect a HTML Page with php to an Active directory.
The Active Directory is only accessable from the System Admin.
So i would have to make a Bind with the Credentials of the Sysadmin and then make a query inside the active directory with the Credentials of the users.
Is that right?
So here is the Code with the i tried to bind with the User Credentials. But it alwasys gives the Echo from Else back "Invalid Credential".
<?php
$ldap_dn = "CN=".$_POST["username"].",OU=EUTM,OU=Users,OU=HQ,OU=ULTIMATE,DC=ultimate,DC=local";
$ldap_password = $_POST["password"];
$ldap_con = ldap_connect("ldaps://192.168.124.40:636");
ldap_set_option($ldap_con, LDAP_OPT_PROTOCOL_VERSION, 3);
if(#ldap_bind($ldap_con,$ldap_dn,$ldap_password))
{
$_SESSION['username'] = $_POST["username"];
header("Location: Startseite.php");
}
else
{
echo "Invalid Credential";
}
?>
EDIT
New Code
<?php
$ldap_dn = "CN=sysadmin";
$ldap_password = "123456";
$ldap_con = ldap_connect("ldaps://192.168.124.40:636");
ldap_set_option($ldap_con, LDAP_OPT_PROTOCOL_VERSION, 3);
if(#ldap_bind($ldap_con,$ldap_dn,$ldap_password))
{
echo "King"
}
else
{
echo "Invalid Credential";
}
?>