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External auth: Bind: Can't contact LDAP server

I’ve setup my Testrail Server in a local LAN environment, and there is also an Active Directory running on Windows Server 2019 within the same subnet 10.140.0.*

Testrail Server:
Windows Active Directory (LDAP Server):

I can use ‘ping’ as well as telnet to from, nothing in between.
But when I tried to login with any account in Windows Active Directory, Testrail Server shows
「External auth: Bind: Can’t contact LDAP server」

From auth.php,

    // Bind to LDAP directory. This does the actual connection attempt
    // and can fail if the configured server is not reachable.
    if (!@ldap_bind($handle, $name, $password))
            _ad_throw_error($handle, 'Bind');

The message doesn’t help anything and I have no idea why Testrail Server can’t contact LDAP Server
Here is my setting of ‘auth.php’

define(‘AUTH_HOST’, ‘’);
define(‘AUTH_PORT’, 389);
define(‘AUTH_DN’, ‘OU=company,DC=XXXXYYYY,DC=com’);
define(‘AUTH_CREATE_ACCOUNT’, true);
define(‘AUTH_FALLBACK’, true);
define(‘AUTH_MEMBERSHIP’, ‘’);

Please kindly help me or teach me how to debug this, thank you