Wordpress Registration by Invite Only -- 2

We have a community WordPress site which we want to keep "closed" by only allowing registration upon invitation. We also only want a member to be able to invite three (3) people (might change in the future). Invitations will not be sent via email. Example Workflow: - An existing User will log in to the system and see their referral code (randomly generated & unique) and also how many invites they have left. Example: Referral Code: AS34SCFE (3 invites left). - The existing user will share the referral code to a person that they want to invite to register. The sharing of the code will not happen via the website. The existing user will share the code in person, or share via WhatsApp, text message, etc. - A visitor will navigate to the website and click on "register". - The registration form will have fields: Username, password, confirm password, Referral code. - - Username will be unique username which the user will be identified with and will be needed to log in (standard WordPress functionality for username). - - Password will be just a password chosen by the visitor that will be needed to log in (standard WordPress functionality for password). - - Confirm password will need to be the same as the password. (to ensure the password is correct). - - Referral code will a unique code linked to the user already on the system that invited the visitor to register. - The existing user will be able to see the username of the person that registered using their unique referral code. - The new user will be able to see the username of the person that shared the invitation code. The referral code can also be inserted in a link which can be used by the person to register (URL to include something like ?ref=AS34SCFE We are open to suggestions if you are able to provide an alternative solution. Maybe the functionality already exists, we won't mind paying if you are able to implement the functionality using existing plugins/code snippets. In short, we need a referral code with a usage limit to limit registrations to invitation only. Looking forward to your bids.