TOC not updating

Hi.

Somehow my TOC is not updating even though I did everything like explained on the Apple website:

Add or remove items in the table of contents

1. If the Document inspector isn’t open, click the Inspector button in the toolbar, then click the Document inspector button .
2. Click the TOC button.
3. Do any of the following:

   Add an item: Click the Add pop-up menu , choose Add Paragraph Style, and choose an option from the submenu.

I applied the header styles H1, H2, H3 etc to the titles of my book but they wont show up on the various pages of my TOC. Can somebody please help me? I'm going crazy already 😟

Thanks in advance,

Chris