Custom Questions - Registration to Pardot

[nfrese]

I am trying to map zoom registration questions (custom questions) to Pardot prospect fields. I can see the custom fields showing up in Pardot, but the mapping is not taking place. 

In this article (https://support.zoom.us/hc/en-us/articles/206003126-Using-Zoom-Webinars-for-Pardot#installing-from-t...), it states that you should map custom_questions as the Zoom Registration Field and custom_question as the Pardot custom field, and that you should only need to do this one mapping in order for it to work for any custom question. However, the issue I am running into is that custom_question is not an option in the Pardot custom field drop down. The actual field itself is showing up and I've mapped to that field, but the data is not syncing. 

These are the two fields I'm trying to get to populate in pardot - they are custom fields that were created by Zoom when the question was created in the zoom webinar.