for me it does not work. I added the site to the trusted site list. Manualy importing the certificate did also not help.
Windows 10 Pro Version 1803 (Build 17134.228)
@damian79 In some rare cases where the Windows environment is up to date (VSTO + .NET), users have reinstalled Outlook in order to create a fresh version for the GoToMeeting plugin to connect with. I don't know that this is the best solution for you, but you are also welcome to call directly into support so that we may document your environment a little better to see where the confusion rests.
Update. Had the same issue today. This fixed it.
Download and instal Visual Studio 2010 Tools
The install the plugin again.
.NET 4.6.1 is also required.