Using Shopify GraphQL API calls with variables

Hello,
I am trying to setup a way for Make to lookup a Shopify inventory ID based on a SKU using a GraphQL API call, and a variable for the SKU. The basic version of this query is very simple, and works fine when I manually feed it a SKU. However, I can’t get this setup to work with a variable. I have tried setting the Variable 1 key options to $sku, or $sku:String!, and then mapped the string option to the Google Sheets cell that I want the SKU stored in. However, no matter what combo of options I try, I cannot get the variables to work. It will throw back errors like: “Variable $sku of type String! was provided invalid value”

I’ve seen another post where people mention needing to use HTTP to make calls, but I’m not sure that’s the case here? And even if so, why? Shouldn’t this module be able to handle query variables?