One time unique access code for registration

Hello,

I am looking to make each new user type in an ‘invitation code’ (that they will have received via hardcopy) before they are able to register. Each user must have a unique invitation code so that we can differentiate the users and confirm they are who they say they are.

I’m not sure if this is possible with s2Member but if it is, please let me know how. I am currently using the free version of s2Member.

Also, if s2Member has a setting that forces every new user to be approved by an administrator, can you please direct me towards that?

If you need anymore details feel free to ask.

Thanks

https://wordpress.org/plugins/s2member/