I have tried to connect to the default MODX provider via Package Mangement on two different sites and both give me the error for
http://rest.modxcms.com/extras/ when I click "Download Extras"
Error "An error occurred while connecting to the Provider: MODx received a blank response from the provider. Please double check your service URL and make sure the provider is a valid provider."
Change the provider domain to modx.com instead of modxcms.com and try again.
Thanks Guys...these are Revo 2.0.8 sites, so I will change that!