How to hide an affiliate program on the service side?

Question

PHP

Let's say:
%USERNAME% follows the link sample.co?r=123 and it has been shortened
sample.co should take the user to a non-affiliate url and set the cookie so quickly that %USERNAME% doesn't notice it.
How would you do it?
Thanks in advance!

Answer 1

What do you mean? We immediately redirect from 123 to the main domain and write the cookie.