ArcGIS Portal not working with LDAP users

I have set user identity store of ArcGIS Portal administration page like following.

{
  "type": "LDAP",
  "properties": {
    "userPassword": "secret",
    "isPasswordEncrypted": "false",
    "user": "uid=gisuser,ou=systemusers",
    "userFullnameAttribute": "displayName",
    "userGivenNameAttribute": "givenName",
    "userSurnameAttribute": "cn",
    "ldapURLForUsers": "ldaps://10.0.0.5:636/ou=users,ou=ags,dc=example,dc=com",
    "userEmailAttribute": "mail",
    "usernameAttribute": "uid",
    "caseSensitive": "false",
    "userSearchAttribute": "cn", 
  }
}

After save the configurations, I tried to add members based on existing enterprise users in Portal. But no users found. The search result is empty whatever I searched.

Why does this happen?