Save project with portal layer added from "Add Layers" tool

When saving a project that contains a layer added from the "Add layers" tool, I get the following error in the console:

Services added through layer addition dialog are only supported if they have been whitelisted by your administrator.

Where do I need to whitelist this? I've added the url root to "Trusted Sites," but no dice. Projects reload without the layer. Any ideas on fixing this?