Script stops working when I duplicate a google sheet - google-apps-script

Question

I've created an order form using a google sheet, with a script to email a pdf of the order to the supplier. I tested it and it worked perfectly fine, so I saved it to the template gallery.
Now when I create a new google Sheet from the template and run the script I get an error - TypeError: Cannot call method "getSheetId" of undefined.
Now if I duplicate the script on the new spreadsheet I just created and call on the duplicated code, it works. Strange thing is when I now try and call the original code, this now works as well. Even stranger when I now delete the duplicated script I just made, the original code stops working again.
I've done this multiple times and I get the same result.
Has anyone got any ideas? Am I doing something completely wrong here?
function emailOrder(){ // this is the function to call
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sh = ss.getActiveSheet();
var shName = sh.getName()
var email = sh.getRange('I8').getValue();
var dates = sh.getRange('V8').getValue();
var reference = sh.getRange('V5').getValue();
var vendor = sh.getRange('B5').getValue();
var contact = sh.getRange('B8').getValue();
sendSpreadsheetToPdf(shName, email , vendor + ' - '+ dates + ' - ' + reference , "Hi " + contact + ", <br /> <br /> See attached order for reference: " + reference + ", <br /> <br /> Kind regards, <br />NAME<br /> PH NUMBER <br /> <br />");
};
function sendSpreadsheetToPdf(pdfName, email, subject, htmlbody) {
var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
var spreadsheetId = spreadsheet.getId();
var url_base = spreadsheet.getUrl().replace(/edit$/,'');
var sheetId = spreadsheet.getActiveSheet().getSheetId();
var url_ext = 'export?exportFormat=pdf&format=pdf' //export as pdf
+ (('&gid=' + sheetId ))
// following parameters are optional...
+ '&size=A4' // paper size
+ '&portrait=true' // orientation, false for landscape
+ '&fitw=true' // fit to width, false for actual size
+ '&sheetnames=false&printtitle=false&pagenumbers=false' //hide optional headers and footers
+ '&gridlines=false' // hide gridlines
+ '&fzr=false' // do not repeat row headers (frozen rows) on each page
+ '&top_margin=0.4&bottom_margin=0.4&left_margin=0.4&right_margin=0.4'; // Margins: set all to 0.4
var options = {
headers: {'Authorization': 'Bearer ' + ScriptApp.getOAuthToken(),}
}
var response = UrlFetchApp.fetch(url_base + url_ext, options);
var blob = response.getBlob().setName(pdfName + '.pdf');
if (email) {
var mailOptions = {attachments:blob, htmlBody:htmlbody}
MailApp.sendEmail(
email,
subject,
"html content only",
mailOptions);
}
}

Answer 1

There are two types of Apps Script documents - Standalone scripts and Bound scripts.
The standalone scripts are not bound to a specific document and are opened and called separately from a document. Thus, if you want call a spreadsheet or sheet within a standalone script, you need to do so by opening the spreadsheet by id or url and the sheet by name
Bound scripts are bound to a specific document ad they can call the bound spreadsheet and its sheets with SpreadsheetApp.getActiveSpreadsheet() and spreadsheet.getActiveSheet(). Bound scripts technically be called separately from https://www.google.com/script/. However, doing so can lead to errors if the bound sreadsheet is not open or is open multiple times. Instead, bound scripts should be open from the UI of the bound document through Tools->Script Editor. Goog practice is to have only one version of the spreadsheet opened, and this recently, before calling the script. Otherwise the determination of the active spreadsheet and sheet can lead to errors.