Hi everyone, if you know what kinds of orders will use third party shipping, you can use an automation rule to charge shipping to a third party account.
The second part of this article goes over how to set that up: https://help.shipstation.com/hc/en-us/articles/205901668Texastr5 commented
This is a very important feature. Please implement it. Its so simple...
Hi! ShipStation is still in the process of understanding the best way to address multiple currencies within a single ShipStation account. We greatly thank you for your patience as we work towards supporting this much-desired feature.