In our lab we have a UC520 connected via a sip trunk to an IP PBX (Selta SamIP). All is working fine but the call forwarding to voicemail from internal phone extensions. The calls received from the outisde, passing through the PBX, are forwarded correctly to the voicemail, as well as calls from the ip phones registered to the UC. The issue arises only when the call is made by a phone registered to the pbx, thus using only the extensions: as soon as the call is forwarded to the cue we receive a fast busy tone. Attached the conf.
Thank you in advance for your help