Server Connect Set Value in a loop

Before I spend more time trying to get this to work, I just want to check I’m doing it right.

I have a loop in Server Connect which goes through all the records. I have a variable called ‘ordertotal’ which needs to hold the total of all the products.

I’ve used the ‘Set Value’ right at the beginning (above the loop) and set it to zero. I’ve then put another ‘Set Value’ with the same name in the loop and put in this value:

{{ordertotal}}+({{detailQty}}*{{queryProductDetails.sizePrice}})

but it’s just giving me zero.

Am I doing something wrong or is it a bug?