I had that same issue.
In the logs it shows:
[15:28:56] [Logger Info] : LDAP authentication unavailable - no licence present that permits this feature.
So I had to follow the steps in this article:
Configuring AMP for Enterprise or Network Usage
Unfortunately after that point, I can no longer log into the instance, either with LDAP users or the original user I set the system up with. ampinstmgr resetlogin does not work reset the login so I’m effectively locked out of the system