This bot is going to manage the trade. Unless you have them added already, check your Steam notifications and accept the friend request. You will then be sent a trade offer which you will need to accept.
The website you were about to visit is not in our whitelist:
There are a lot of imitation phishing sites and so-called item generators out there, and the safety of our users takes priority! If you see this message when you thought you were going to a genuine website, you probably weren't...
Alternatively if the site actually is legitimate, open a ticket and we'll whitelist it.