To charge a third party for a FedEx, UPS, OnTrac, or DHL Express shipment, you just need to enter the information for that specific order.
First, find the order on your Orders tab, and double-click its order number to open up the Order Details pop-up.
Then, make sure you've got a FedEx, UPS, OnTrac, Canada Post Commercial, or DHL Express service selected. Once that's verified, look for the Other Shipping Options section on the right of the pop-up.
Now, locate the Shipping Account dropdown menu and choose "Third Party."
Now, you'll see the Account #, Billing Country, and Billing Zip fields display so that you can enter in the information.
Once you've input all the necessary information, you can Close the pop-up to save your changes.
Please note that while ShipStation is unable to display shipping rates when billing shipping charges to another party, the other party will be billed according to their own carrier agreement. Depending on the carrier, there may be an additional fee for using third party billing. For example, UPS adds a 2.5% fee.
When you ship the order, the resulting shipment will be charged to the FedEx/UPS/OnTrac/DHL Express account number you specified.