curl --request POST \
  --url https://api.iotools.cloud/v1/tool/permutation-combination-calculator \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "n": "5",
  "r": "2"
}
'

{
  "tool": "permutation-combination-calculator",
  "tool_version": "1.0.1",
  "outputs": {
    "results": [
      {
        "metric": "Permutations P(n, r)",
        "value": "20"
      },
      {
        "metric": "Combinations C(n, r)",
        "value": "10"
      },
      {
        "metric": "n!",
        "value": "120"
      },
      {
        "metric": "r!",
        "value": "2"
      },
      {
        "metric": "(n − r)!",
        "value": "6"
      }
    ]
  },
  "credits_used": 3,
  "credits_remaining": null
}