I created a custom entity that can be populated using entity forms. One of the fields of the entity is the Node ID of the content it was attached to. It's auto-populated and hidden.

I'd like for all the corresponding submissions to be shown when a person visits the page. I am trying to do this using views. Basically, I want to filter the submissions based on the nid field of the entity matching the nid of the content URL for the content. However, when I go to create the view and state that I want to show an entity, Content: NID is not an available option in the Contextual filter.
What should I do?