curl --request POST \
  --url https://api.iotools.cloud/v1/tool/survey-sample-size-calculator \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "population": "",
  "marginError": "5",
  "confidenceLevel": "95",
  "proportion": "50"
}
'

{
  "tool": "survey-sample-size-calculator",
  "tool_version": "1.0.1",
  "outputs": {
    "sampleSize": "385",
    "breakdown": [
      {
        "metric": "Confidence level",
        "value": "95%"
      },
      {
        "metric": "Critical z-score",
        "value": "1.9600"
      },
      {
        "metric": "Margin of error (e)",
        "value": "±5%"
      },
      {
        "metric": "Expected proportion (p)",
        "value": "50%"
      },
      {
        "metric": "Required sample (Cochran)",
        "value": "384"
      },
      {
        "metric": "Population (N)",
        "value": "Unknown / very large"
      },
      {
        "metric": "Recommended minimum sample",
        "value": "385"
      }
    ],
    "sensitivity": [
      {
        "margin-of-error": "±1%",
        "sample-cochran": "9,604",
        "sample-with-fpc": "—"
      },
      {
        "margin-of-error": "±2%",
        "sample-cochran": "2,401",
        "sample-with-fpc": "—"
      },
      {
        "margin-of-error": "±3%",
        "sample-cochran": "1,067",
        "sample-with-fpc": "—"
      },
      {
        "margin-of-error": "±4%",
        "sample-cochran": "600",
        "sample-with-fpc": "—"
      },
      {
        "margin-of-error": "±5%",
        "sample-cochran": "384",
        "sample-with-fpc": "—"
      },
      {
        "margin-of-error": "±7%",
        "sample-cochran": "196",
        "sample-with-fpc": "—"
      },
      {
        "margin-of-error": "±10%",
        "sample-cochran": "96",
        "sample-with-fpc": "—"
      }
    ]
  },
  "credits_used": 3,
  "credits_remaining": null
}