From what I can find on my end, it looks like checkout rates are not yet available. But your desire to have this feature on the Shift4 integration is great to know!
If I hear anything to the contrary, i'll come back here to update you accordingly 🙂
yes - i also would like to display real time rates for this cart solution. i have tried the other 4 that ShipStation is currently integrated with for displaying live rates but to be honest, those 4 carts do not hold a candle to the robustness of Shirt4's SaaS system.