Hello,
You are using the statement wrong.
The second argument for SetElementAdd is an element parameter with the range Spaces (same as the set you provided for the first argument).
You can declare a new element parameter by adding a new identifier. You can also update the declaration of the set Spaces with the attribute "Parameter". Specify a name there, say ep_Space.
Now your for loop call will be SetElementAdd(Spaces, ep_Space, iterNr).
The logic is, an element parameter is a data structure to store a single element in a set. So, each element parameter is linked to a specific set so that it can hold the elements of that set.
SetElementAdd is adding a single element to the set Spaces. So, you store that single element in the element parameter ep_Space whose value will be equal to iterNr.