Generating Text with Gemini Pro in Apps Script

function generateContent(text, API_KEY) {
  const url = `https://generativelanguage.googleapis.com/v1beta/models/gemini-pro:generateContent?key=${API_KEY}`;
  return JSON.parse(UrlFetchApp.fetch(url, {
    method: "POST",
    headers: {
      "content-type": "application/json"
    },
    payload: JSON.stringify({
      contents: [{
        parts: [
          {text}
        ]
      }]
    }),
  }).getContentText())
}

const response = generateContent("Hello world!", API_KEY);
const text = response.candidates[0].content?.parts[0].text;