When ShipStation notices that you are shipping via USPS and there is a lower rate available, we will display an extra column on your rate confirmation screen. This column will show you the label cost and account balance details for the lower cost postage provider.
You can decide to use the optimized/recommended rates on a case-by-case basis by selecting the radio button above the extra column. But if you always want ShipStation to select optimized/recommended rates for your USPS shipments automatically, you can check the "Always optimize my USPS rate selection" box on the rate confirmation screen.
If you do this, the lowest cost USPS provider will automatically be used to create your shipping labels.
Feel free to manage this automatic rate selection setting at any time by following these steps.
Head to your Account Settings (the gear icon in the upper right).
Next, select Shipping and then Carriers & Fulfillment from the sidebar on the left.
Then, look for the "USPS Rate Selection" section, and click Manage USPS Rate selection options.
Here, you can simply check or uncheck the box for "Always optimize my USPS rate selection" as needed, and Confirm.