Register the 3PL's carrier accounts in ShipStation via the Carriers API or the Connect Carrier endpoint, providing the account credentials and carrier code
Create a ShipStation automation rule that selects the cheapest rate across configured carriers for orders meeting defined criteria (weight range, destination zone, service level)
For carriers not natively supported, configure a custom carrier using ShipStation's Custom Carrier integration, mapping the carrier's label API responses to ShipStation's tracking fields
Use the ShipStation Rates endpoint to fetch available rates for a shipment before label creation, and select the optimal service programmatically based on business rules
Create the label via the ShipStation Labels endpoint with the selected carrier code and service code, then push the resulting tracking number back to the originating platform order via a webhook or direct API call
Set up ShipStation webhook subscriptions for ship notification and shipment voided events to keep downstream order management systems synchronized
Known gotchas
ShipStation rate shopping only compares carriers that are fully configured with active account credentials; inactive or misconfigured accounts are silently excluded from rate results
Custom carrier label formats must produce a tracking number in the response body in the exact field ShipStation expects; deviations cause tracking to appear blank in the UI and on customer emails
Voiding a label in ShipStation does not automatically void the label with the carrier; the void must also be submitted to the carrier's API separately within the carrier's void window
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp