Question regards to Custom Post-In API

Hi, I have a problem with Custom Post-In API.

We are using Custom Post-In Webstore and we tried to print multiple packages with FedEx Ground shipping service.

When I post the order data with the XML format into ShipRush. It messed up and mixed up for the package order. (Each package have different dimension and weight)

Is there any way to make it the same as what I've added on XML?

Thank you.