Basically, the form for invite requests is published directly at my-discourse-website.com/login page
Users need to fill out a short questionnaire and specify why they want to join our platform (we are a group engaged with community outreach, public legislation proposals etc.)
There is also a form on an inner custom page accessible by members where they can request an invite for a friend. All invite requests are reviewed by moderators.
Actually, I’ve also got a reply from Jeff Atwood with regards to adding a file to web root:
So I will be seeking other options. Thank you for the tips about Memberful and WP plugins, I’ll explore them further.