Mongodb – How can I generate user's QR-code in node.js?

First off, I need some suggestions regarding QR code in my app.

I am building a parking-management app in node.js in which there are different tables like user, booking, parking etc.

Now, Users will search for parking availability and book one parking-slot and based on that details the QR code will be generated. now whenever user go to that parking place he needs to show that QR-code to the parking attendant. The parking attendant will scan the QR code and will verify the details and the in database there is a field called isStarted will become true(Initially it was false). So the questions are:

1. Do I need to generate QR-code in the back-end and store it to the database or It will be generated from the front-end Side?(I think I don’t need to generate it in the backend I just need to decrypt it)

2. If it generates on the front-end then what approach should I take to decrypt it?

3. It is not related to the QR-code but still asking. I want to notify the merchant(parking-owner) about the details of user who wants to park their vehicle in the merchant’s space. How can I do that with node.js? I have some code already written by someone which is as following but I don’t understand what it is.

    let notification_data = {
      name: `${owner.basicInfo.fullName}`,
      date: dayjs(req.body.date).format("MMM DD, YYYY"),
      startTime: req.body.startTime,
    };
   
    let { title, body } = notificationTypes.addBooking(notification_data);
   
    let data = {
      senderId: req.data.id,
      receiverId: req.body.walkerId,
      title,
      body,
    };
   
    sendNotification(data);
   

Can anyone here help me with above queries?