If you need to ship only part of an order, you can divvy up the order into multiple orders that you can ship at different times.
On the Orders tab, select the order that you need to split, then find the Other Actions menu in the actions bar, click it, and then choose Split Order.
In the new window, notice that ShipStation automatically adds a suffix (e.g. "-1" or "-2") on to the order number, so that it's easier to tell any split orders apart from the original. Please note that you should remove the suffix and retain the original order number when splitting orders from BigCommerce or Magento. These selling channels (and any others that support partial shipments) will only recognize the original order number when we let them know an order has partially shipped.
Also, it's easy to modify the tags on the split-off order, in case you want to add a "Backordered" or similar tag.
Identify which items and quantity you’d like on the new order, and input the cost of the items that you are moving from one order to another. Enter the Amount Paid, Shipping Paid, and Tax Paid if you would like to split the totals.
Click Confirm and you'll now have two orders!