zabbix_agentd: listener #1 [waiting for connection]

[HJ_SK]

I instaled from scratch zabbix 7 server on raspberrypi 4 w bookworm (v12) , up and running ok as it seems.
I installed zabbix-agent on several RPi 3 witch bullsEye (v11).
The ZBX icon on host from these RPi3's stays grey, the example of zabbix-server as green.
Asking status on zabbix-agent i got the folowing output :
sudo systemctl status zabbix-agent

zabbix-agent.service - Zabbix Agent
Loaded: loaded (/lib/systemd/system/zabbix-agent.service; enabled; vendor >
Active: active (running) since Sat 2024-09-14 14:02:00 CEST; 1h 12min ago
Process: 31303 ExecStart=/usr/sbin/zabbix_agentd -c $CONFFILE (code=exited,>
Main PID: 31305 (zabbix_agentd)
Tasks: 6 (limit: 1595)
CPU: 4.358s
CGroup: /system.slice/zabbix-agent.service
├─31305 /usr/sbin/zabbix_agentd -c /etc/zabbix/zabbix_agentd.conf
├─31306 /usr/sbin/zabbix_agentd: collector [idle 1 sec]
├─31307 /usr/sbin/zabbix_agentd: listener #1 [waiting for connecti>
├─31308 /usr/sbin/zabbix_agentd: listener #2 [waiting for connecti>
├─31309 /usr/sbin/zabbix_agentd: listener #3 [waiting for connecti>
└─31310 /usr/sbin/zabbix_agentd: active checks #1 [idle 1 sec]

Sep 14 14:02:00 BE-33-PowerTest systemd[1]: Starting Zabbix Agent...
Sep 14 14:02:00 BE-33-PowerTest systemd[1]: Started Zabbix Agent.

So why I got the message :zabbix_agentd: listener #1 [waiting for connection]
Has it maybe to do with on server Bookworm and on agent Bullseye?

After long times seeking can't find any about : zabbix_agentd: listener #1 [waiting for connection
Aynone an idea?
Thanks for helping out!
Harm