How can you bill a customer immediately for a change to a subscription within the same billing cycle?

Billing a customer immediately for a change to a subscription within the same billing cycle can be effectively accomplished by setting the proration behavior to "always_invoice" and ensuring that the pending_update hash transitions to "paid."

When you configure proration_behavior to "always_invoice," Stripe generates an invoice that includes any prorated charges or credits needed to adjust the customer's billing for the changes made to the subscription. This means that any adjustments due to the subscription change will be reflected in a new invoice that is issued immediately. By ensuring that the pending_update hash moves to "paid," you confirm that the newly created invoice is successfully processed, thereby completing the billing immediately.

This method effectively manages the customer’s expectations by providing them with a clear invoice for the updated charges and ensures that the billing is executed promptly without additional complications. Other options do not effectively ensure an immediate payment process or rely on complicating actions like issuing refunds, which could lead to confusion.