Why getContentText() comes before JSON.parse
UrlFetchApp.fetch() returns an HTTPResponse object, not a string. The first time I skipped getContentText() and passed the response object directly to JSON.parse(), it silently parsed to null and the sheet wrote nothing. You need raw = response.getContentText() to get the actual body as a string, then JSON.parse(raw) turns it into a JavaScript object or array.
The URL must be publicly accessible or accept an API key via a query parameter or Authorization header. Add headers like this: UrlFetchApp.fetch(url, { headers: { Authorization: 'Bearer ' + token } }). Apps Script's UrlFetchApp quota is 20,000 calls per day on a free Google account, 100,000 on Workspace.