Add ProjectHuddle Capabilities to a Subscriber Role
ProjectHuddle uses it's own roles for website commenting so it's not open to just anyone. The reason for this is sometimes people use the subscribers role for customers or members but don't necessarily want to give them access to ProjectHuddle. As an example, customer who purchases something from your site for instance shouldn't automatically be allowed to access the website widget and leave comments. Here's some information on roles:
A Guide to Roles, Capabilities and Permissions
However, you can add ProjectHuddle capabilities to the subscriber role if it fits better for your site. You can use a plugin like WPFront's user role editor to accomplish this:
Once you install the plugin, navigate to Roles > All Roles and click on the "subscriber" role to edit. Then in the "Copy From" box, select "Project Client" and click Apply. This will apply Project Client capabilities to subscribers.
You'll also want to make sure the users are added as "Project Members" so they have access to the website project. Otherwise you can open up access to everyone under ProjectHuddle > Settings and check "Unsilo Project Access":