Yep, it is Amazon service. Here is the email that I got from Amazon. Make sure you order book as Request copy.

Dear , Your request for a proof version of ‘Задачи и теоремы линейной алгебры’ is ready for checkout. Requested copies will be available in your Amazon shopping cart for the next 24 hours. You can complete checkout by clicking the following link:

Proceed to Checkout

Questions? Learn more on our help page.

The Kindle Direct Publishing Team