Webhooks + Google Sheets

function doPost(e) {
  try {
    var sheet = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
    var payload = JSON.parse(e.postData.contents);

    var leadData = payload.data;
    var formData = leadData.form || {};

    // Build a flat record: fixed metadata columns first, then all form fields
    var record = {
      "Timestamp":     new Date().toISOString(),
      "Form Name":     leadData.formName     || "",
      "Submission ID": leadData.submissionId || "",
      "IP Address":    leadData.ip           || ""
    };

    // Dynamically include every field present in the submission
    for (var key in formData) {
      if (formData.hasOwnProperty(key)) {
        var field = formData[key];
        record[key] = field && field.value !== undefined ? field.value : "";
      }
    }

    // Read existing headers (row 1), or start with an empty list
    var lastCol = sheet.getLastColumn();
    var headers = lastCol > 0
      ? sheet.getRange(1, 1, 1, lastCol).getValues()[0]
      : [];

    // Append a header column for any field not yet in the sheet
    var keys = Object.keys(record);
    keys.forEach(function (k) {
      if (headers.indexOf(k) === -1) {
        headers.push(k);
        sheet.getRange(1, headers.length).setValue(k);
      }
    });

    // Write the row in the same order as the headers
    var row = headers.map(function (h) {
      return record.hasOwnProperty(h) ? record[h] : "";
    });

    sheet.appendRow(row);

    return ContentService
      .createTextOutput("Success")
      .setMimeType(ContentService.MimeType.TEXT);

  } catch (err) {
    return ContentService
      .createTextOutput("Error: " + err.toString())
      .setMimeType(ContentService.MimeType.TEXT);
  }
}