How are you getting the values for URL and Path variables? Are you passing it or do it get from an expression?
That's possibly where I'm missing something. I'm adding the variables in the variable window with the URL and the Path as the values for each and then adding the variable names to the Arguments.
Do I have to add the variables as expressions? I think I've missed doing something here.
You need to if you've to get values on the fly. The variables have a property called EvaluateAsExpression which should be set to true and then give expression under expression builder available from variable properties window.