Invite team member functionality in MERN website

I am building a website using mern stack where every user who signs up gets their own subdomain according to the username they entered.

What I have done so far:

1. Users can create an account and get their subdomain according to the username they entered while signing up.
2. Owner of the organization can send invites to the team members using email by filling out a simple form where they need to enter the email of the team member.

Now, I would like to know how I can add the team member to the organisation's workspace so they have full access to the workspace. Basically, I don't know what to do after sending an invite.

Please give me some insights on how this can be achieved.

Thanks.