If you have trouble in the checkout page, in the order summary, when you select the payment method cash on delivery, the row of fee of cash on delivery is not shown , while the cost is added to the total order.
https://www.loom.com/share/6e733479d71d4f0684ba100b0f7b99da
For this issue, If you are using onestepchekcout extension, it is not theme bug. So it's out of our support scrope.
We recommend you to contact extension provider to ask for supporting.