Youtube to Post: Trying to save YouTube url to custom field

Hi, I’m loving the plugin, thanks so much! I am using it to make posts from YouTube videos, and I am having trouble getting the youtube URL saved into a custom field. This is what I’ve entered in the “Post Custom Fields” section: youtube_url => %%item_url%% It creates a custom field called youtube_url, but the value saved is %%item_url%%, not the actual Youtube video URL. I tried some different variables and none of them worked. See images.