Ubuntu Payment Service
The Ubuntu payment service handles transactions for Ubuntu Software Center, Ubuntu One, the Canonical store, and other systems where people can purchase things from Canonical. It is hosted at https://pay.ubuntu.com/ . Development is hosted at https://launchpad.net/canonical-payment-service .
Purchase issues, refunds, and other payment FAQs
Update after Ubuntu 16.04
Support for purchases is available from firstname.lastname@example.org.