UrBackup discovery does not work, logs are quite empty

I cannot get discovery to work.

Expected result: client is added to server after clients receives broadcast messages from server.
Actual result: client is not added to server. Client logs do not mention receiving broadcast message. Server logs do not mention sending broadcast message and do not indicate failure.

Which mistake am I making?

UrBackup server: 185.233.174.134 (vlan5)
UrBackup client: 185.233.174.200 (ainalrami)

Client

Configuration: urbackupclientctl set-settings -k internet_mode_enabled -v false -k computername -v "{{ inventory_hostname }}"

Settings:

[root@ainalrami urbackup]# cat /etc/sysconfig/urbackupclient | grep -v \#
LOGFILE="/var/log/urbackupclient.log"
LOGLEVEL=warn
LOG_ROTATE_FILESIZE=20971520
LOG_ROTATE_NUM=10
DAEMON_TMPDIR="/tmp"
RESTORE=disabled
INTERNET_ONLY=false

Firewall:

[root@ainalrami ~]# iptables -nvL | grep 185.233.174.134
    0     0 ACCEPT     tcp  --  *      *       185.233.174.134      0.0.0.0/0            tcp dpt:35621
    0     0 ACCEPT     tcp  --  *      *       185.233.174.134      0.0.0.0/0            tcp dpt:35623
   30   870 ACCEPT     udp  --  *      *       185.233.174.134      0.0.0.0/0            udp dpt:35622

Receiving broadcast messages:

[root@ainalrami urbackup]# tcpdump -i any udp port 35622 -n
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes
16:42:39.957237 IP 185.233.174.134.35623 > 255.255.255.255.35622: UDP, length 1
16:42:40.020541 IP 185.233.174.200.35622 > 185.233.174.134.35623: UDP, length 41
16:43:29.988141 IP 185.233.174.134.35623 > 255.255.255.255.35622: UDP, length 1
16:43:30.061452 IP 185.233.174.200.35622 > 185.233.174.134.35623: UDP, length 41
16:44:20.019286 IP 185.233.174.134.35623 > 255.255.255.255.35622: UDP, length 1
16:44:20.496630 IP 185.233.174.200.35622 > 185.233.174.134.35623: UDP, length 41
16:45:10.050296 IP 185.233.174.134.35623 > 255.255.255.255.35622: UDP, length 1
16:45:10.281597 IP 185.233.174.200.35622 > 185.233.174.134.35623: UDP, length 41

Log (LOGLEVEL=debug) after receiving broadcast message:

[root@ainalrami urbackup]# tail /var/log/urbackupclient.log
2020-03-22 15:35:21: FileSrv: Binding ipv6 UDP socket at port 35622...
2020-03-22 15:35:21: FileSrv: done.
2020-03-22 15:35:21: Started UrBackupClient Backend...
2020-03-22 15:35:21: FileSrv: Servername: -ainalrami.vlan5.hosts.cyberfusion.space-
2020-03-22 15:35:21: FileSrv: Server started up successfully
2020-03-22 15:35:21: FileSrv: UDP Thread started
2020-03-22 15:35:22: Looking for old Sessions... 0 sessions
2020-03-22 15:35:22: Internet mode not enabled
2020-03-22 15:35:22: Final path: /
2020-03-22 15:35:22: Final path: /home

Server

Internet settings:

Firewall:

root@vlan5:/etc/ferm# iptables -nvL | grep 185.233.174.128
    0     0 ACCEPT     tcp  --  *      *       185.233.174.128/25   0.0.0.0/0            tcp dpt:55415

Log (LOGLEVEL=debug) few seconds after receiving broadcast message:

root@vlan5:/etc/ferm# tail /var/log/urbackup.log
2020-03-22 16:37:24: Binding to interface ens18 (ipv4) for broadcasting...
2020-03-22 16:37:24: Broadcasting on ipv4 interface ens18 addr 185.233.174.134
2020-03-22 16:37:25: UrBackup Server start up complete.
2020-03-22 16:37:25: Looking for old Sessions... 0 sessions
2020-03-22 16:37:25: Server started up successfully!
2020-03-22 16:37:25: Downloading version file...
2020-03-22 16:37:26: Downloading version file...
2020-03-22 16:37:26: Downloading server version info...
2020-03-22 16:37:26: Downloading dataplan database...

This problem does not occur when firewall on backup server is turned off, but my firewall has been configured according to the ports mentioned in the Server administration manual…

It seems like UDP port 35623 should be opened for clients to the server.

Perhaps this should be added to the administration manual, section 10.3 (under “The Client binds to following default ports (all incoming)”).