Jira service desk customer unable to add comment in confluence space

Summary

JIRA service desk customer unable to add comment in confluence space although the space has been given anonymous access.

Step to replicate

1. Create an user with access 'Restricted Portal';
2. Create a space in Confluence;
3. Set Anonymous access on the space (Space tools) and give them can add comment permission;
4. Try accessing the homepage of the space (created on step 3) using the user 'Restricted Portal' (created on step 2);
5. Try to add comment

Observed Behaviour

User unable to add comment

Expected Behaviour

User able to add comment