It’s sometimes handy (e.g, in test suites) to have a JSON string hardcoded. If you want to interpolate it to insert a variable, use $$””” and then {{ }}.

In this example my interpolation expression is the variable ratingUnitNumber:

var ratingUnitNumber = "test";
var cloudEvent = $$"""
{
  "id": "5565db35-01a9-4596-b611-9b26d2210c6e",
  "source": "https://s4h-dev.blah.govt.nz",
  "type": "nz.govt.blah.s4.ratingunitchanged",
  "subject": "blah",
  "data": {
  "ratingUnits": [
    {
      "ratingUnitNumber": "{{ratingUnitNumber}}"
    }]
  },
  "time": "2024-03-11T23:09:27.5683052+00:00",
  "specversion": "1.0"
}
""";

Hopefully that helps someone.