Ok cool
I’d just try a few variations without the MyDomain and alternating your backslash and forward slash separators if you haven’t already.
It may just be your proxy setup. You may be able to start a dialog with your network engineers to enable https access to plugins.gradle.org by trying out some command line tools (something they can reproduce easily)
See my previous post here Cannot apply plugin with the "plugin DSL" when running behind an authenticated proxy
Good luck