VRL Flatten function error

[satellite-no]

I keep getting and error with the flatten function trying to flatten the object below. Is it too complex? a bug? anyone have any suggestions. If I do is_object() it returns true so it meets the expectations of the flatten funtion.

error[E110]: invalid argument type
  ┌─ :1:9
  │
1 │ flatten(.p)
  │         ^^
  │         │
  │         this expression resolves to one of string, integer, float, boolean, null, array or object
  │         but the parameter "value" expects one of array or object
  │
  = learn more about error code 110 at https://errors.vrl.dev/110
  = see language documentation at https://vrl.dev
  = try your code in the VRL REPL, learn more at https://vrl.dev/examples

example

{
  "active": 1,
  "agents": [
    {
      "active": 1,
      "agentId": 113253,
      "agentName": "Windsor Edge Agent",
      "dateStart": "2024-11-18 14:10:00",
      "metricsAtEnd": "Active",
      "metricsAtStart": "Error: \"Connection timed out after 5001 milliseconds\"",
      "permalink": "https://app.thousandeyes.com/"
    }
  ],
  "alertId": "348688fa-7de1-4113-a97f-4b8675907bd0",
  "apiLinks": [
    {
      "href": "https://api.thousandeyes.com/",
      "rel": "related"
    },
    {
      "href": "https://api.thousandeyes.com/",
      "rel": "data"
    }
  ],
  "dateStart": "2024-11-18 14:15:00",
  "metadata": {
    "version": 1
  },
  "permalink": "https://app.thousandeyes.com/",
  "ruleExpression": "((probDetail != \"\"))",
  "ruleId": 123,
  "ruleName": "Proxy Error Alert",
  "severity": "INFO",
  "suppressed": 0,
  "testId": 123,
  "testName": "my-test-1",
  "type": "HTTP Server",
  "violationCount": 1
}

[pront]

The type of the .p above is not obvious to me because it doesn't appear in the JSON example. Can you share a https://playground.vrl.dev/ example?