RestQuery Block can access input values from other blocks but throw "is not defined"

I'm trying to use the RestQuery block to make an external API call as part of a workflow. I am passing data from a previous step in the workflow, defined here as "recipient." For some reason the block is able to access the data from the input, as evidenced by the greentooltip showing the values, yet it throws a "is not defined" error.

When I run the workflow, it appears to be unable to retrieve the recipient properties and executes the query with blank values.