Dovecot connection to ldap timeout

[ewok2]

Hello
I have install a postfix / dovecot / rouncube mail server on a virtual Ubuntu 22.04 machine.
The mail seem's to work
Buut when trying to connect dovecot to my ldap (openldap on another vm) it does not work...
I look in all mail roundcube and dovecot log but don't see any error.

The login windows seem's trying to connect without success. I get a "504 Gateway Time-out"
And the last log indicate the same :

On ldap side I get some log saying connection is done :

slapd[3449]: conn=1007 fd=16 ACCEPT from IP=192.168.0.roundcube:40916 (IP=0.0.0.0:389)
slapd[3449]: conn=1007 op=0 BIND dn="cn=admin,dc=mydomain,dc=net" method=128
slapd[3449]: conn=1007 op=0 BIND dn="cn=admin,dc=mydomain,dc=net" mech=SIMPLE bind_ssf=0 ssf=0
slapd[3449]: conn=1007 op=0 RESULT tag=97 err=0 qtime=0.000009 etime=0.000071 text=

on dovecot side I get :

auth: Debug: Loading modules from directory: /usr/lib/dovecot/modules/auth
auth: Debug: Module loaded: /usr/lib/dovecot/modules/auth/lib20_auth_var_expand_crypt.so
auth: Debug: Module loaded: /usr/lib/dovecot/modules/auth/libdriver_mysql.so
auth: Debug: Loading modules from directory: /usr/lib/dovecot/modules/auth
auth: Debug: Module loaded: /usr/lib/dovecot/modules/auth/libauthdb_ldap.so
auth: Debug: Read auth token secret from /run/dovecot/auth-token-secret.dat
auth: Debug: ldap(/etc/dovecot/dovecot-ldap.conf.ext): LDAP initialization took 0 msecs
auth: Debug: auth client connected (pid=4502)
imap-login: Debug: SSL: where=0x10, ret=1: before SSL initialization
imap-login: Debug: SSL: where=0x2001, ret=1: before SSL initialization
imap-login: Debug: SSL: where=0x2002, ret=-1: before SSL initialization

Any idee what is wrong and what can bloc the connection ?
Thanks for help