Empty table of contents - even thought I set all the headings correctly

Idk what to do… I have set my main headings as heading 1, and headings that are 1 level below them, as heading 2.
When I insert the table of contents, all I get is this:

Any ideas?

By default, ToC takes its content from outline levels of paragraphs, so first of all - check that your header paragraphs have outline level set to corresponding value. Normally, that should be done with applying header paragraph styles, but if the styles are edited to remove the levels (for unclear reason), or paragraphs themselves are formatted manually with same effect (after styles already applied), this may happen.

Note that for “header” you should read “heading”.

You should also check out Tools - Outline numbering and make sure that Level 1 is linked to the Heading 1 style.

This happen with every document downloaded like ODT from Google Docs (a bug), for some strange reason, for headings 1 to 6 only. Always have to fix going to where Floris point: http://i.imgur.com/tMASm7T.png

In libreoffice 6.0.7 I had to go to Tools > Chapter numbering to fix this issue. I had exactly the same situation as @PabloAB described after I’ve exported the document from google docs.

When the “Table of Contents, Index or Bibliography” dialog opens, one must check the “Additional Styles” checkbox, click on the “Assign styles” button, and then click on the buttons to assign heading levels to table-of-contents levels. This functionality is nice, but the default settings don’t make much sense.

Thank you. After a day of not being able to progress, your answer solved my problem. I had exported from Google Docs and couldn’t understand why I had this problem with both ODT and DOCX. Very much appreciated!

Thank you. As I cannot upvote your answer I put a comment (I need 5 points).