At the time of the order, an authorisation of the amount you have ordered on the chosen payment method is carried out. Your payment method is only charged once the order is closed, based on the products actually shipped.
If one or more products cannot be sent, the relative cost is not charged.
If a missing product is replaced with one at a lower price, the system will automatically charge you the lower price. If the missing product is replaced with another of a higher price, no surcharge will be applied to the value of the product ordered.
Any authorised amounts which are not actually charged are released according to the timing established by the chosen payment method.