Node ID is not appearing
Turns out nid in Drupal 8 is now listed as ID - and it is listed liked this: 
Title - ID and Category - content.  It appears on the view as Content: ID. I put this in Fields and made it hidden.  I added a relationship to my other content type.  Then for contextual filter I used the Content:ID with the relationship. Under When filter is not available, I picked Provide default value: Content ID from URL. And then the view worked.