Add Merchant Rates for USPS

[todd7]

A USPS representative just contacted us. This representative said we should switch shipping platforms and use GrandShipper because they offer Merchant Rates and ShipStation does not. When will ShipStation offer Merchant Rates for USPS Priority Mail packages?

https://usps.my.salesforce.com/sfc/p/#j0000000GyYH/a/t0000002lr9Y/gpV98CU4BvHuLc4yRS.1adZwHiP.4FknKb...