app-script-template

function doPost(e) {
  let sheetName = "Page1"
  let sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName(sheetName);
   if (!sheet) {
    return ContentService.createTextOutput("Error: Sheet not found");
  }
    let newRow = sheet.getLastRow() + 1;

  let rowData = [];
  
  rowData.push(new Date());  // Timestamp
  rowData.push(e.parameter.FirstName);
  rowData.push(e.parameter.LastName);
  rowData.push(e.parameter.Age);
  rowData.push(e.parameter.Gender);
  rowData.push(e.parameter.Country);
  rowData.push(e.parameter.PhoneNumber);
  rowData.push(e.parameter.Email);
  rowData.push(e.parameter.Message);
  
  sheet.getRange(newRow, 1, 1, rowData.length).setValues([rowData]);
  
  return ContentService.createTextOutput('Form submission was successful. Thank you. We will get back to you within 24 hours');
}