The snippet installation is different based on the site you're installing it.
- Marketing sites: users can't sign in to these sites, e.g. landing pages, blogs, marketing sites, promotional pages.
- Web-Apps: users can sign into them, although they may also be able to visit these sites anonymously, without an account.
Are you using only one container for all your website? If that's the case, you should follow these instructions.
In case your site is separated into two containers (One for the marketing site and one for your web-app site), you should follow these instructions.
For information about Containers, you can check the Google Tag Manager documentation