getFolderById works fine in apps editor, but won't in related spreadsheet

I have a spreadsheet which aims to generate invoices. One sheet per invoice, and some checkboxes to manage the content. One of them is designed to save sheet as pdf file into a dedicated folder of the GDrive of the same account.
Here is my code:

function saveInvoiceIntoGDrivePDF() {
const currentSpreadSheet = SpreadsheetApp.getActiveSpreadsheet();
const paramSheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Paramètres généraux");
const currentSheet = currentSpreadSheet.getActiveSheet();
const invoicesStorageFolderOnGDriveId = paramSheet.getRange('B30').getValue();
DriveApp.getFolderById(invoicesStorageFolderOnGDriveId); const authorizationToken = ScriptApp.getOAuthToken();
SpreadsheetApp.getUi().alert("Got Auth Token!");
const exportLink = "https://docs.google.com/spreadsheets/d/"+currentSpreadSheet.getId()+"/export?format=pdf&size=a4&portrait=true&scale=4&top_margin=1.00&bottom_margin=1.00&left_margin=0.50&right_margin=0.50&gridlines=false&printnotes=false&pageorder=2&horizontal_alignment=CENTER&vertical_alignment=TOP&printtitle=false&sheetnames=false&fzr=false&fzc=false&attachment=false&r1=0&r2=40&c1=1&c2=6&gid="+currentSheet.getSheetId();
const invoicingYear = SpreadsheetApp.getActiveSheet().getRange('J5').getValue();
const invoicingMonth = SpreadsheetApp.getActiveSheet().getRange('N6').getValue();
const customerName = SpreadsheetApp.getActiveSheet().getRange('J9').getValue();
const indexFacture = SpreadsheetApp.getActiveSheet().getRange('J7').getValue();
const invoicePDFFileName = "Invoice_"+invoicingYear+"_"+invoicingMonth+"_"+customerName+"_"+indexFacture+".pdf";
const exportParams = { method:"GET", headers:{Authorization:"Bearer "+authorizationToken}, muteHttpExceptions:true };
var invoicePDFContent = UrlFetchApp.fetch(exportLink, exportParams).getBlob().setName(invoicePDFFileName);
invoicesStorageFolderOnGDrive.createFile(invoicePDFContent);
}

Set authorizations into appsscript.json as following:

{
"timeZone": "Europe/Paris",
"dependencies": {
},
"exceptionLogging": "STACKDRIVER",
"runtimeVersion": "V8",
"oauthScopes": [
"https://www.googleapis.com/auth/script.external_request",
"https://www.googleapis.com/auth/drive",
"https://www.googleapis.com/auth/spreadsheets.readonly",
"https://www.googleapis.com/auth/spreadsheets"
]
}

This function, like many others, is triggered by a checkbox in the "management area" of each sheet, with the label "Save as PDF in Drive".

The problem is that this function works like a charm when running it from the Apps scripts editor, but won't gather drive permissions from the appsscript.json.

I understand there are limitations on authorizations, but what I can't figure out is that, as the script projet is (from my understanding) attached to the spreadsheet, why it can run from the editor but not from the spreadsheet it has been designed for? What is the interest to allow to write a script which won't work in "real world"?

And, if this is a strong authorization issue, is there a way to have Google "accept" this script, as it only creates new files in the same account it belongs to?

Any help appreciated,
Many thanks,
Emmanuel

Tried all I could from documentation and forums (but could hardly get "outdated" posts).

The issue is that this spreadsheets is to be run by people whith little computers knowledge, and for the moment, they have to:

1. Click on the "open pdf in a separate tab"
2. Download pdf setting the name manually
3. Upload file from their computer to GDrive

This is (obiously) painful from their point of view, and very little satisfying as this is the very last straight line of my "application".

> checkboxes to manage the content. One of them is designed to save sheet as pdf

It sounds like you are using an onEdit(e) simple trigger to run the saveInvoiceIntoGDrivePDF() function.

onEdit(e) runs in a context where it cannot access any personal information nor call services that would require authentication. All DriveApp methods require authentication, so they cannot be called from onEdit(e).

To make it work, use an installable trigger instead of a simple trigger, or run the saveInvoiceIntoGDrivePDF() function through some other means, such as a button, a custom menu item, or a sidebar.