We can send live rates for customers to choose from at checkout with Shopify. The feature that provides this functionality is called Checkout Rates. Review our Send Rates to Store Checkout article to learn how to set up and use this feature.
For other selling channels, ShipStation cannot send live rates for your customers to select at checkout at this time.
Many selling channels provide access to plug-ins so you can provide live rates from your carrier accounts to your customers during the checkout process. You will need to contact your selling channel for details.
Stay tuned! We are working with our partners to expand these options to more selling channels soon!