I'm very impressed with PBXes so far and I'm so close to having everything working as I would like. However, I've had trouble initiating transfers via the SIP method (i.e. using the transfer button as oppose to DTMF *2, ##, etc.). I'm using Groundwire softphone, which is otherwise excellent, but transfers sent using the built-in buttons fail. I contacted Groundwire support, who were helpful and asked for the logs, which show that the transfers fail because a "404 not found" response is returned when a transfer is initiated using REFER, in this case to extension 204, via email@example.com. The Groundwire support said there's not much they can do without knowing why PBXes is sending a not found response.
Any help would be much appreciated!