When orders are merged, the following actions take place automatically:
A new order is created, combining all items from the prior orders into one new order.
The merged orders are canceled and archived.
Extra shipping charges are refunded to original form of payment. Read Shipping refunds for merged orders article to learn about how shipping refunded are determined.
Customer is sent a notification that their orders have been merged.
Depending on the payment provider and whether a refund was issued, the customer may also receive separate refund notice.