We upgraded our pbx to v15 around a month ago, which has had its fair share of issues we are hoping service packs will address, but we have a persistent issue with some, but not all of our windows softphones. After the phone system upgrade, we upgraded our windows phones to v15 as well. Some have been working fine since and some have not worked since. All the windows phones are on the same LAN as the server and all the client machines have the same AV and firewall settings. And all of the machines having the issue were working fine on PBX & softphone v12.5 On some of our softphones we get the message: "3cx Phone for Windows could not establish a connection to the 3cx phone system web api. As a result features like contacts and presence information will not be available" and the phones indeed don't have presence information or contacts. I tried to narrow down what the differences were between working and non working. I noticed that all of the working phones were on version 15.0.57336 and the non working phones on version 15.0.56772. There appears to be no way to have the softphone check for an update manually, and the version that is coming out of the downloads section is still 15.0.56772 I uninstalled via control panel and reinstalled version 15.0.56772 and resent the welcome email, after clicking on the config file, it detected the available update and prompted to install. We had problems with 4 clients and I got all of them up to the 15.0.57336 this way. After the update, the presence information was now available. For two of the clients, this seems to have resolved the issue. However, on the other 2, after the system got rebooted, i'm seeing the same message, on the version 15.0.57336.