Why I don't get my configured Active Checks?

[AlBoPo]

Hello,

I've defined an item provided by a custom zabbix agent active.

The item configuration is described here https://i.imgur.com/RkBuVjf.png.

From my agent here is what I can see when it asks for active checks to the zabbix server 3.4.12:

AVB[4301]: Send JSON string {"request":"active checks","host":"LL709601401410"}
AVB[4301]: Received JSON string {"response":"failed","info":"host [LL709601401410] not found"}

Could you tell me why please?

[Atsushi]

As the message says, the hostel named "LL709601401410" is not registered.
Please check with the Host name of the host registered in frontend of Zabbix server.
It is not with Visible name to compare.

[AlBoPo]

As you can see in the joined screenshot (https://i.imgur.com/RkBuVjf.png), the host actually exists or maybe I don't really understand what you mean by 'registered' as I'm new in Zabbix.

and LL709601401410 is declared in 'Host name' field, not in 'Visible name' field.