Add Other Shipping Options to ShipNotify object.
It would be helpful if the ShipNotify object included information about orders billed to a third party account.
When you ship with UPS or FedEx you have the option to bill the shipment to a third party. We often use this when drop shipping. This is displayed in ShipStation under Other Shipping Options (see screenshot), but is not included in the ShipNotify payload sent to a custom store.