I guess you added the component to your theme and you have already tried to refresh the site in the browser after that (Just mentioning that because I sometimes forget).
Did you try the preview button of the theme? That can be helpful to check for a conflict with another component (Though I think it’s unlikely)
You can also try to add the text that the button in the composer menu adds to the post manually
<div data-theme-toc="true"> </div>
Does that work?