When you first receive an order, the order can be found under Pending Payment. This can be viewed at any time, and you can also send reminders to retailers to pay for the order.
Retailers are also able to cancel an order at this point.
After an order is paid, the order moves to the Paid section within Orders. This is when the stock count is reduced - after the order has been paid.
If either the you or retailer needs to cancel the order, the stock will be increased on both Modalyst and Shopify. Always make sure that your inventory is high enough to avoid over selling a product.