[Private] plugin information

Hello.
I am creating this site:
www.mortiscausa.it
I would like only certain users to register on the site whom I will contact via email or sms.
I would like to find a way to prevent other people from signing up.

To do this, I thought of assigning each user a code that I will send by email or text message so that when they sign up they can enter the code in a specific field to be filled in. Subsequently, when I extrapolate the table of users, I will check if the code matches and I will delete or not approve the user.
I also thought about the possibility of sending (if possible) a registration link (with the customer code inside) valid for each user ....
What I would like to know is if there is an easier way to do this automatically (not for single user otherwise for 10000 users it would be impossible) with your plugin and if it is not possible if you know someone who does it or if at most if it is possible customizing the code of a plugin because this is my first site that I am creating without having any knowledge.
I hope you can help me.
Thank you

your plugin:

User Verification