Displaying code

I have a strange issue and I don’t know where the fault lies.

According to this:

https://en.support.wordpress.com/code/posting-source-code/

I should be able to show source code.

I have also asked this here:

https://stackoverflow.com/questions/46718436/showing-source-code-in-a-wordpress-blog-post

In short, I can’t display source code.

The page I need help with: [log in to see the link]