I have updated the source code to address nested fields like links.website, delta.year.

function getCoinInfo(coin, field_name = 'rate', currency = 'USD', trigger) {
  // Replace with your actual API key
  const apiKey = 'de524e1a-2b81-48e8-86de-03a8046e88b2';
  const url = 'https://api.livecoinwatch.com/coins/single';
  const headers = {
    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:123.0) Gecko/20100101 Firefox/123.0',
    'x-api-key': apiKey,
    'Content-Type': 'application/json',
  };

  const payload = {
    "currency": currency,
    "code": coin,
    "meta": true
  };

  const response = UrlFetchApp.fetch(url, {
    "method": "post",
    "headers": headers,
    "payload": JSON.stringify(payload)
  });

  const data = JSON.parse(response.getContentText());

  // Check if field_name contains '.', indicating a nested structure
  if (field_name.includes('.')) {
    // Split the field_name to traverse through the nested object
    const fields = field_name.split('.');
    let currentValue = data;
    for (let i = 0; i < fields.length; i++) {
      if (currentValue[fields[i]] !== undefined) {
        currentValue = currentValue[fields[i]];
      } else {
        // Handle cases where the path does not exist
        return `Field "${field_name}" not found`;
      }
    }
    return currentValue;
  } else {
    // Direct access for non-nested fields
    return data[field_name];
  }
}

function force_update() {
  var sheet = SpreadsheetApp.getActive().getActiveSheet();
  var now = new Date();
  // Format the date and time. Example: "YYYY-MM-dd HH:mm:ss"
  // Adjust the format as needed. 
  // The time zone is set to "GMT" here, but you should replace it with your desired time zone.
  var formattedDate = Utilities.formatDate(now, "GMT", "yyyy-MM-dd HH:mm:ss");
  sheet.getRange("B2").setValue(formattedDate);
}