It follows the principle where a visitor click on a link on
website1.com and get redirects to
website2.com with some additional path params which helps GA track if the visitor is same and GA maintain it's session.
I have been looking around a lot and couldn't find a solution on how can I track a visitor which comes on
website1.com through ads and then leaves (And/Or open new tab) and immediately/later goes on to
website2.com and make some purchase. I am not targeting to maintain session per user but at least I need to know if it's the same visitor which goes there and converts.