The total shipping is calculated as (13.61 + 1.32) = 14.93 which is correctly displayed in order details. Indeed, the tax is applied to the shipping cost because that's how Walmart submits the order information into Linnworks (right-click on the order - View - View order xml). Screenshot is attached. If it's not correct please contact Walmart to find out why did they send the wrong information.
We are trying your system and we realized that the orders that are being downloaded from Walmart do not match the real total in Walmart.
The problems seems to be in the Sales tax numbers, for example I am attaching a screenshot of the order and the information in Walmart: