Calcurates for Magento and Adobe Commerce allows you to connect USPS via Stamps.com or other carrier accounts to Calcurates. Connecting a carrier account with Calcurates requires account credentials and IDs, depending on each carrier. In your Calcurates account please proceed to
Menu > Carriers and in the carriers grid click
"Connect Carrier" in the Actions column for the needed carrier.
For more detailed info please read our
"How to connect your USPS account" user guide which will give you more instructions on how to connect your Stamps.com account to Calcurates for Magento.