I am building iredmail system with high availability referring to docs.iredmail.org/haproxy.keepalived.glusterfs.htm. After installation and configuration,  I could create a mailbox on the iredamin of first email server with syncing it to second email server. However, I could not create a mail box on the second email server(see attached photo). I have enabled the debug mode of LDAP log on both email serves, but did not find any errors.  The configuration of LDAP on both email servers is as follows. How do I solve the problem?

1st mail server:

/etc/ldap/slapd.conf:

moduleload syncprov
index entryCSN,entryUUID eq
overlay syncprov
syncprov-checkpoint 100 10
syncprov-sessionlog 200
"/etc/ldap/slapd.conf" 248L, 8807B

2nd mail server:

/etc/ldap/slapd.conf:

syncrepl rid=001
         provider=ldap://mail1:389
         searchbase="dc=example,dc=com"
         bindmethod=simple
         binddn="cn=vmail,dc=example,dc=com"
         credentials=password
         schemachecking=on
         type=refreshOnly
         retry="60 +"
         scope=sub
         interval=00:00:01:00
         attrs="*,+"