How to get Headings and Paragraphs Appear in Reading Order

I'm making a PDF accessible for assistive technology and have hit a very basic problem: when I look at the tagging and the reading order in the PDF, none of the doc headings or text is tagged. I've done all of the export tagging in paragraph styles, ticked the necessary boxes when exporting to interactive PDF, and arranged the layers panel / articles panel accordingly. Any help would be greatly appreciated. 

<Title renamed by MOD>