If you have multiple USPS postage providers connected to your ShipStation account, ShipStation can display the USPS service options in two ways:
By postage provider: This option will list each postage provider in the Service drop-down menu with all of their active services so you can choose a specific service from a specific provider.
By carrier: This will list all available USPS service options under the single heading USPS.
To change how your services list is displayed, click the action menu next to the Service drop-down menu:
If this action menu is not present, that means you do not have multiple USPS providers connected to your ShipStation account.
Here is an example of how your Service drop-down menu will look for each option: