Does ShipStation charge me for my postage?

This will depend on whether your label is from a ShipStation Carrier or from one of your own connected carrier accounts.

For labels using ShipStation Carriers, ShipStation is considered the postage provider. The first time you create a label with one of these carriers, you'll be prompted to enter the payment method to use for your label fees.

For labels using your own connected carrier accounts, that carrier acts as postage provider, not ShipStation. Charges for these labels will go through your carrier account and appear on your regular invoice from that carrier.