What happens when I press buy button in software center?

Just for my curiosity, what are processes happening,when I press buy button in software center ? . I just noticed that it updates software cache when I pressed buy button. It means it adds a temporary repository for that app?

After clicking on the Buy button, Ubuntu Software Center will prompt you to login or create an Ubuntu Single Sign On account.

Ubuntu Single Sign On (Ubuntu SSO) is a service provided by Canonical Ltd that allows users to login to multiple websites and access multiple services. Use your Ubuntu SSO to login to the following Canonical websites:

• Launchpad
• Ubuntu One
• Ubuntu Shop

PURCHASING SOFTWARE

If you already have an Ubuntu Single Sign On account, proceed with your software purchase:

1. In the More Info screen, click on Buy
2. Login to your Ubuntu Single Sign On account
3. Review the Quantity, Description and Amount of your software purchase
4. Enter your Billing address
5. Enter your Billing information
6. Click Review Payment to proceed (or cancel to stop)
7. Review your payment information
8. Click Submit Payment to purchase software¹

^{1Source:Ubuntu Software Center Documentation}

If the App is free, but shows the buy button and $0.00 like the app in the image below, after you login, you will get

And below is the final outcome. The App was installed without paying a dime.

For repositories, and how they integrate with USC seeIntegration with Ubuntu Software Center.