Same issue here, ER7206 v1.0, firmware 1.4.0 Build 20231114 Rel.36220, configured Active Directory + other services without problems, in case of TP-Link the only thing I get is "Failed to connect to the LDAP server."

  @Tedd404 Yes, the server is correct, it's just the internal IP of my Windows Active Directory server. The message is the same, no matter what I change in my settings.

For now it's hard to tell if I have anything useful to share, as it does not work for me. Just wanted to add the "me too" answer, maybe somebody from TP-Link reads forums and will publish any guide how to connect it to Active Directory.

  @Tedd404 Sorry, but you're wrong. Active Directory is the implementation of LDAP. I connected LDAP software to Active Directory many times (including OpenVPN Access Server). I can browse it using LDAP tools. According to Wikipedia https://en.wikipedia.org/wiki/Active_Directory

" Active Directory uses Lightweight Directory Access Protocol (LDAP) versions 2 and 3, Microsoft's version of Kerberos,^[6] and DNS.^[7] "

  @2Dr In Another Thread I got the response, that the buildin-LDAP of Windows-AD is not supported.

You need to setup a third-party ldap-relay then, turning the Microsoft LDAP into specification-conform LDAP.

I cannot follow this recommendation, as i'm using the buildin-ldap for many other applications, but maybe they all just went the extra mile to support AD (as one if the most common usecases) while tp-link didnt.

  @2Dr same issue here, that is a stunning tplink miss that it simply cannot query AD natively, requiring an intermediate solution. Pretty useless like that,