You can view what a carrier charged you for a specific label in a few ways:
Check the Carrier Fee column in the Shipments Grid.
If you do not see the Carrier Fee column, go to the Columns drop-down menu and check the box next to Carrier Fee to add that column to your grid. ShipStation adds new columns to the end of the Shipments grid, so you may have to scroll horizontally to view it (click and drag the column to move it to another location).
Open the Shipment Details screen - this can be done from either the Shipments grid or the Order Details screen - and view the label details panel. The label cost is next to the shipment tracking number.
For accounts on the High Volume plan, there is an additional per-label fee for all labels created with Your Carriers (ShipStation Carrier labels are exempt from this fee). The per-label fee is billed on your monthly invoice, which you can view by going to
Settings > Account > Payments & Subscription and then clicking the Past Invoices link.