Corosync IAX2 2 Servers + BLF


I’ve 2 Servers connected via IAX2 and wants to BLF a Line from a phone, what is registered to the other Server.

I have installed an implemented Corosync successfuly in Asterisk.
Under Asterisk CLI “corosync show members” shows the 2 Asterisk Servers.

I’ve tested it by adding this to the first Server in the dialplan:
exten => foo,hint,Custom:abc:

And on the 2nd Server I’ve do command via CLI:
dialplan set global DEVICE_STATE(Custom:abc) INUSE

And then on the first Server this hint is synchronized.
“Core show hints” shows custom:abcd as “InUse”.

But now, there are Sip Phones at the 2nd Server, I want to watch.
I can call them via IAX2/Server2/NUMBER.
But how can I watch via hint the extension ??

Can anyone please help me ?
Thank you.

Greetings from Germany !