ldaps issues

I have an issue trying to connect to a server using ldaps.

I have the following configuration:

domain controllers: ldaps://<the ldap domain>
port: 636
Use TLS: false

In the test tool I get:

[INFO] Checking domain controller ports:
[ERROR] – ldaps://<the ldap domain>:636 – FAILED

The server does not have a self signed certificate. Am I supposed to do something else in order to allow ldaps connections? The server is which my wordpress is running uses debian and is a fresh installation.

https://wordpress.org/plugins/active-directory-integration/