Enable guest access
From MoodleDocs
You must first enable guest access on your site and then in your course.
Guest access to the site
1. Log in with your administrator account
2. From the left panel (the Navigation drawer) click Site administration
3. Click Users and then from Permissions, click User policies
4. Tick the box Auto-login guests
5. Click the Plugins" tab and scroll down to Authentication
6. Click Manage authentication
7. Make sure the Guest login button is set to 'Show'