Getting 403 Forbidden Error After Setting up Custom Domain

I am just after publishing a site with a custom domain. is appearing as it should but is giving me a 403 error. I have already checked the DNS records and have unpublished it and published it again. Unsure how to address this issue.

Here is my site Read-Only: LINK
(how to share your site Read-Only link)

Did you follow the publishing guidelines and set WWW to be default?