If you're using Rich + Markdown, canonical links need to be added differently.

Click on the engine icon at the bottom of the post.

A small window should pop-up:

Now you can add the canonical link.

You only need to add the link address like this:

https://yourblog.com/add-canonical-link

And remove the rest.

To find the canonical path, do the following:

• Press F12
• CTRL + F and search for "canonical"

You should see something such as:

<link rel="canonical" href="https://yourblog.com/add-canonical-links">

I hope this helps!