In v0.90v of the 1999 editor, it's easier to add Disqus comments to a blog.

1. Edit the template and add [%disqusComments%] after the divChatLog section of the body. It might already be there if you created your site after Aug 29, 2016. Here's a screen shot that illustrates the placement.
2. Choose Settings from the System menu at the right edge of the menu bar. Click on the Disqus tab.
3. Click the checkbox to enable the feature. Screen shot.
4. Optional. If you have created your own Disqus group you can enter its ID in the space provided, or you can accept the default 1999io group, created for 1999.io users.
5. Click OK.
6. Edit a post on the site and update it. Click on the Eye icon for the post. if it worked you should see a comments section at the bottom of the post.

If you have questions post a comment here.