How to insert voice occupied unreachable?

Good Morning,
I would insert the voice BUSY unreachable, and the first of these messages I would like to enter a custom message.
What should I write in sip.conf to enter these functions?

thanks dell’attenszione given to me
thanks in advance

Messages produced by Asterisk are controlled by extensions.conf, not sip.conf. To produce them with Asterisk you use Playback, with the appropriate standard or user supplied message file. To produce them upstream, on unanswered calls, you use Hangup with an appropriate ISDN cause code.

It is difficult to say more because we have no idea what is in your dialplan.

thanks for the quick response,
I have no idea on what to do.
here is my extensions.conf

exten =>1000,1,Playback(demo-echotest);
exten =>1000,2,Echo;
exten =>1000,3,Playback(demo-echodone);
exten =>1000,4,Playback(demo-thanks);

exten => _1XXX,1,Answer()
exten => _1XXX,n,Dial(SIP/${EXTEN},40,tr)
exten => _1XXX,n,Hangup

exten => pstn,1,Verbose()
exten => pstn,n,Dial(SIP/1002&SIP/1003,40,tr)
exten => pstn,n,Hangup

exten => _1XXX,n,Dial(SIP/${EXTEN},40,tr)

Test ${DIALSTATUS} and/or ${HANGUPCAUSE} after this line:

exten => _1XXX,n,Dial(SIP/${EXTEN},40,tr)

and call Playback with the appropriate messages.

Note that the call to Hangup is redundant.

I did not understand what I have to write:

exten => _1XXX,1,Answer()
exten => _1XXX,n,Dial(SIP/${EXTEN},40,tr)
exten =>1XXX,n,Playback(all-circuits-busy-now)

is that right?

Also look at extensions.conf.sample that comes with the source.

If that information is not sufficient, you need to hire a consultant, as peer support forums assume that you have a basic understanding of what you are doing.