• we can add and remove a chargeable service to existing boooking
• have a payment link (Stripe) for an extra payment if required
• and I believe refund is already supported through order balance when it becomes negative (I hope)
• it has to work for any OTA, not only for direct bookings

This is useful if you want to charge for early check-in or late check-out, for example. And any other additional services an agency may have.

Best regards,
Alex