Convert CSV string to Array in Mapping - create-nodeset-from-delimited-string ?

Summary: I've got an API which requires an array of string into a parameter called base. I want to use a Comma Separated Value passed into my integration which I convert into the array of string at mapping time.

I can achieve this in Postman, but trying to pass a single string like : "GBP","USD" or ["GBP","USD"] does not work in OIC. From reading all the posts and watching vids I can find I believe I probably need to use create-nodeset-from-delimited-string but I cannot get this to work.

I've added a For Each around the base parameter and then tried to use the function but it errors each time.