Can’t embed channel

I would like to embed channel, or what I want is to have something like latest videos or most watched in widget.

When I try to embed single video it works, but when I try to add channel I get this

“Sorry, that does not seem to be a link to an existing video. Please confirm that the link works in your browser, and that the owner of the video allowed embed sharing permissions (otherwise, contact the owner of the video to allow embedding). Then copy that full link in your address bar to paste here. If you are sure your link is correct, then your API key may be too restrictive”

I have no restrictions on my API key, I tried channel and I tried single video. I still get the same error.

I am trying to put it in widgets to be shown on all pages and posts.

Because single video works, I think my API key works as well, but don’t know how to solve problem with channel. Or, if you have better idea for latest video or most watched with your plugin in widget, please suggest.

The page I need help with: [log in to see the link]