I am having some issues adding a modifier to a line item via the sdk. I can add the line item to an order through the sdk no issue but then I have tried using the orderconnector.addLineItemModification and all I keep getting is ClientException error. My current process is using orderconnector.addVariablePriceLineItem to add the line item to the order which works great but then using orderconnector.addLineItemModification gives me an error. Is there a different method I should be doing this?