This is a test website. Nothing is charged. Clicking "Enroll Credential" launches a PaymentRequest window from the cross-origin iframe to create a credential. Then, copy the credential into the text box (this transaction would happen in the back-end in a production environment). Then, clicking "Pay $0.01" creates a Secure Payment Confirmation request from the iframe with the given credential. This tests two things, (1) that the iframe can activate the SPC UI, and (2) that the iframe's SPC request can exercise an existing credential that was created in a different frame.
If this is your first time, visit https://lumbar-brick-soup.glitch.me/ to install the credential enrollment payment handler.
Based on the Secure Payment Confirmation explainer.