This seems to be a known issue in the latest stable release. To use mydomoticz we need to switch to the latest beta or wait for the next release.

Please refer the following thread for further information - viewtopic.php?f=47&t=7764&start=360

Same issue for me while enabling mydomoticz feature. Tried Domoticz build 3.5877 on both Window 10(64Bit) & Raspberry Pi 3 (Jessie Lite).

Log - Error: PROXY: StartThread(): Exception: resolve: Host not found (authoritative)