httpPostJson Event IsoDate Attribute

I’m not sure why this doesn’t work with httpPostJson. If I replace ${evt.isoDate} with a simple string, it works fine. Is there something I have to do with formatting to make it work? I’ve tried adding single/double quotes, but the httpPostJson call fails.

def params = [
uri: “”,
body: [
eventdate: “${evt.isoDate}”,
name: “test”

I just figured it out. no need for the ${…}. Just evt.isoDate works.