when making an outbound call and the person you are calling is busy/engaged on another call, your phone will just hang up the call without any indication to the person being busy.
To get an audible busy, please disable the 'eary-disconnect' option from the SIP interfaces on the Patton.
Telephony -> Call Router -> Interfaces -> SIP <interfaces>
Also ensure DSS1 is set as the ISDN protocol on the E1/T1/BRI interface.
also pleasse check wiithin 3CX management Console > Settings > Generial "Tab Global Options" Play busy prompt when extension is busy is tcked.