How to distribute many games at once

https://www.steamgifts.com/about/faq

Why is there a limit to the number of gifts I'm able to give away?
We limit the number of gifts a user can create for security purposes, and to prevent a new user from potentially posting a large number of invalid gifts to the site. When you create giveaways and your gifts are received, this number will increase. At that time you'll be able to create giveaways with a greater number of copies, and more simultaneous giveaways.

If you're a developer, you can also let support upgrade your account. See bottom of the FAQ.

спасибо