Hi, Without wishing to stray too far into the world of development here ... We're building a softphone that should (like the 3cx mobile client) be able to detect whether or not other extensions are 'online' or not. We have the code to do this, but haven't been able to test it as the requests it sends to subscribe to the presence of our extensions are being rejected (489: Event Package Not Supported). Are there any ports in particular that we need to open/settings we need to change in the PBX in order to get this working? We're using v15 of the phone system. All other functionality works fine. Thanks in advance for your advice.