One of automatic (default) or manual. See ConfirmationMethod.

When confirmationMethod is automatic, a PaymentIntent can be confirmed using a publishable key. After next_actions are handled, no additional confirmation is required to complete the payment.

When confirmationMethod is manual, all payment attempts must be made using a secret key. The PaymentIntent returns to the RequiresConfirmation state after handling next_actions, and requires your server to initiate each payment attempt with an explicit confirmation.