I've been working with content types and creating custom forms for each of them with Nintex Forms 2013 on-prem. When I create a generic "Item" custom content type, I can add it to a list, create a new item, and the option for adding attachments is within the ribbon. As soon as I edit this same content type and publish the content type's form with Nintex Forms, the option is no longer there for attachments. The attachments control also does not show up in any of the form control options on the left when searching for it.
What am I missing here?