OK, Hillary, is "Chap" the name of the para tag that is only in the header of the master page?
Or is it the name of the para tag in the text flow that formats the name or number of the chapter?
If the former, it'll never show up in the TOC because it only exists on a Master page.
To be listed in the TOC, the tag needs to be in the main text flow.
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Most of the time, when people set up a book file, would use one tag to format the chapter title. Then they would include the name of that tag when they set up the TOC. To put the name of the chapter in the header or footer, you'd format a Running H/F 1 (or any other number) so that it contains a string like <$paratext[ChapterTitle]>
Art