database ldap uri "ldap://localhost:389" bindmethod=simple binddn="cn=root,o=Test,c=IT" credentials="password"
^^^ this is not a valid slapd-ldap(5) configuration; use slaptest -d config to find out what is wrong, and check slapd-ldap(5) for valid directives.
The fact that lookups work while writes don't, indicating that authentication is required sounds like your client is not binding.
p.
Ing. Pierangelo Masarati OpenLDAP Core Team
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