'X-MS-TOKEN-AAD-ID-TOKEN': property doesn't exist

[BobGerman]

I'm trying to get Graph Token extension working in an Azure function using the instructions in this repo and I keep getting this error:

Error while accessing 'X-MS-TOKEN-AAD-ID-TOKEN': property doesn't exist.

I've checked the documentation 5 times and done a bunch of web searches; need this urgently for a demo. Any chance you can help? Am I missing something easy?
Note I added the extension via the command lines in the article on Github, and deployed via VS Code.

Thanks!

Here is my function.json:

{
  "disabled": false,
  "bindings": [
    {
      "authLevel": "anonymous",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "token",
      "direction": "in",
      "name": "graphToken",
      "resource": "https://graph.microsoft.com",
      "identity": "userFromRequest"
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}