Bind to Azure LDAPS via Azure AD Domain Services always returns Invalid credential

I've read a lot of messages in these forum questions, but I've not find any right answer to my problem.

I've configured my domain "domain.onmicrosoft.com" following the documentation steps here described:

- https://docs.microsoft.com/en-us/azure/active-directory-domain-services/active-directory-ds-admin-guide-configure-secure-ldap

- https://docs.microsoft.com/en-us/azure/active-directory-domain-services/active-directory-ds-getting-started

My target was cloud-only user accounts configuration.

After task 1 to 4 I've managed to connect to LDAP server on port 636 and got response (good!)

I volontary missed the task 5 because I don't need to authenticate users on the manages domain

What I want to do now is to test with a generic LDAP client (Softerra, ldap.exe) the bind alwais give me "Invalid Credential"

res = ldap_simple_bind_s(ld, 'CN=administrator.email,OU=AAD DC Administrators,DC=domain,DC=onmicrosoft,DC=com', <unavailable>); // v.3
Error <49>: ldap_simple_bind_s() failed: Invalid Credential
Server error: 80090308: LdapErr: DSID-0C09042F, comment: AcceptSecurityContext error, data 52e, v2580

I've tryed these DNs as Principal value for LDAP binding:

CN=administrator.email,OU=AAD DC Administrators,DC=domain,DC=onmicrosoft,DC=com'

CN=administrator.email,OU=AADDC Users,DC=domain,DC=onmicrosoft,DC=com'

CN="administrator name",OU=AAD DC Administrators,DC=domain,DC=onmicrosoft,DC=com'

CN="administrator name",OU=AADDC Users,DC=domain,DC=onmicrosoft,DC=com'

CN=other.administrator.email,OU=AAD DC Administrators,DC=domain,DC=onmicrosoft,DC=com'

administrator.email

What is wrong? 

Thanks