Busy tone not deliver

when callers are reached to a person who is on the call , they don`t get busy tone , and they hear normal ringing tone . the called party also start to ring behind the current call.
please provide a clue on where do I need to seek the issue?

In the called party’s phone.

If you come back to Asterisk, you need to seek it in the logs and configuration, without which we can’t help.

At the moment, it appears that the destination device allows multiple calls, so it is probably a VoIP device, although not necessarily a SIP one.

Asterisk technology drivers often have options to limit the number of concurrent calls, and you can also use the group count features to do so entirely in the dalplan.

as I read through sip.conf.sample of asterisk files , it suggest that callcounter need to be set instead of call-limit.
and I did so , but same problem exist.
of course when the callers are send to queue , this problematic functionality happens.

For a queue, you need have ringinuse=no

I already implement that


As already mentioned before, it looks like the called party has a phone with more than one line.
You should disable the second line on the phone itself or set call-limit=1 in the configuration of that peer on Asterisk side.

More details can be provided when you share the asterisk config and phone models.