Hello, please review the following link: Carrier Switches and Tracking Data for Third-party Shipping Integrations

That might help.

@olgakonanykhina22 - Thanks for the info.  It still doesn't provide the level of detail needed for connecting to ShipStation.  Not sure if ACU discontinued this after 22R1 launch.

Hi Steven, the ‘Custom’ carrier was made available for ISVs building their own carrier integrations.  I would recommend reaching out to the primary contact via the link below for additional documentation and to see if there are plans to enable their carrier using this feature. 
https://www.acumatica.com/acumatica-marketplace/shipstation-ecommerce-shipping-solution/