What orders can be synced to ShipStation?

To sync to ShipStation, the sales order cannot be a credit memo or quote and it must be scheduled.

Much like any other shipping workstation integration within Acctivate, the ShipStation sync will only send shipping information for orders that are scheduled and are not credit memos or quotes.  In other words, at least one line item must be have a scheduled quantity greater than zero.  Since Completed or Booked orders don't have scheduled line items, they will not be synced.

Naturally, the ShipStation integration has to be properly set up to function as well.  Take a look at this article to confirm it's been set up correctly if you're not sure.