How to create a table of contents correctly

I read the LibreOffice wiki and created this: Image of my table of contents

I need to have both “Síntoma: Estornudos” and “Síntoma: Tos” as indexes of the table of contents. Unfortunately, I have not succeed in doing it. What should I do?

Thanks in advance!

Possibly you did not treat both “Síntoma: Estornudos” and “Síntoma: Tos” in the same way with the same styles. May I see the document that you made the Table of Contents from?

@KenMcAllister: Thanks for your answer! What do you exactly wish to see?

@oweng: Thank you very much for your answer. It worked when I created the TOC again after applying some heading levels. You are right when you say that “Estornudos” may have been marked by me when I first tried to make it work. Problem is solved.

Thanks for confirming. I have converted my comment into an answer.

@pablofiumara if you could create a simple document with just the two heading entries and a table of contents (ToC) showing one heading being included and the other not, that would probably be sufficient. From the screenshot it appears that only the term “Estornudos” has been marked (bookmarked?) and that the ToC is based on bookmarked entries rather than heading levels.