Maybe this helps.
https://itch.io/docs/creators/download-keys
There is no private message system on itch. Why would you give away the the game to random people, anyways?
Also, there is no beta testing on itch. Games are marked as in development, sometimes for years, and people have full access to whatever the developer uploads or even sells. One might call that beta test. Contrary to steam, you can assume for each and every game the tag "indie" and the equvivalence of early access until specifically an actual release is announced. Some people mistake the words and "release" their unfinished projects, as the act of doing so could be called releasing. To make it even more complicated, even release status does not automatically mean, that there won't be significant updates anymore.
The keys above are used, so people do not have to pay for a paid game. Like for promotion. You can use this for beta testing, of course. But if you do public beta test, why not just publish the game as "in development"?