Invite codes

Hey everyone , i've been a member of indie hackers for a while , and i love the community as internal knowledge that this platform provides or various aspects of business and software development.

I've never got the chance to introduce someone to this amazing platform , and i've recently been keen on inviting a friend of mine who's an entrepreneur but never contributed enough to get an invite code.
What exactly are the actions need to be taken in order to receive one ?