Print to shipstation connect from the ShipStation API
A better feature (that could accommodate more users and would cost less to build than building an adapter for IOT, linux, etc systems) would be allowing print directly to "ShipStation Connect" connected printer via the shipstation api. Something like https://ssapi.shipstation.com/shipments/pritnlable, with a body that includes the ID of the printer that the current ShipStation web API is using to print and the base64 from createlabel api.
Most users can deploy a windows VM to have that feature and then any REST available IOT app can use the API to print. You already have the endpoint (you need to use it for your web app). You just need to add a endpoint for users to use that feature through the API.