Sending Email of Multiple Google Sheets as Excel Attachment (As 3 x Sheets or 1 with Sub Sheets) from App Script

function sendEmailWithAttachments() {
  var spreadsheetId = SpreadsheetApp.getActiveSpreadsheet().getId();
  var sheetName = "Sheet1"; // Change this to the name of the sheet you want to export
  var url = "https://docs.google.com/spreadsheets/d/" + spreadsheetId + "/export" + "?format=xlsx&" + "gid=" + SpreadsheetApp.getActiveSpreadsheet().getSheetByName(sheetName).getSheetId();
  var params = { method: "GET", headers: { "authorization": "Bearer " + ScriptApp.getOAuthToken() } };
  var blob = UrlFetchApp.fetch(url, params).getBlob().setName(sheetName + ".xlsx");
  var message = {
    to: "email@domain.com",
    cc: "email@domain.com",
    subject: "Email Subject",
    body: "Email Body",
    name: "Your Name",
    attachments: [blob]
  };
  MailApp.sendEmail(message);
}

This code sends an email with a single attachment, which is the exported contents of a specified sheet in the active spreadsheet. To send multiple attachments, you can use the following code:

function sendEmailWithMultipleAttachments() {
  var spreadsheetId = SpreadsheetApp.getActiveSpreadsheet().getId();
  var sheetNames = ["Sheet1", "Sheet2", "Sheet3"]; // Change this to the names of the sheets you want to export
  var attachments = [];
  sheetNames.forEach(function(sheetName) {
    var url = "https://docs.google.com/spreadsheets/d/" + spreadsheetId + "/export" + "?format=xlsx&" + "gid=" + SpreadsheetApp.getActiveSpreadsheet().getSheetByName(sheetName).getSheetId();
    var params = { method: "GET", headers: { "authorization": "Bearer " + ScriptApp.getOAuthToken() } };
    var blob = UrlFetchApp.fetch(url, params).getBlob().setName(sheetName + ".xlsx");
    attachments.push(blob);
  });
  var message = {
    to: "email@domain.com",
    cc: "email@domain.com",
    subject: "Email Subject",
    body: "Email Body",
    name: "Your Name",
    attachments: attachments
  };
  MailApp.sendEmail(message);
}

This code sends an email with multiple attachments, which are the exported contents of multiple sheets in the active spreadsheet. You can also use a trigger to send the email with attachments automatically on a schedule. For example, the following code sends an email with attachments every day at 8 AM:

function createTrigger() {
  ScriptApp.newTrigger("sendEmailWithAttachments")
      .timeBased()
      .everyDays(1)
      .atHour(8)
      .create();
}

Be sure to replace "sendEmailWithAttachments" with the name of the function you want to run.