Receive live notification and show it as a popup
So I want to create an app, where on the one phone a QR-Code is displayed. In the QR-Code are some information like an id and a decryption key. If another user scans that QR-Code, a pop-up should appear on the phone where the QR-Code is shown, to "authorize" the other phone.
Is this possible with Googles Firebase, or do I have to manually create sockets in order for the device to receive the "notification"? Or do I have to build the back-end myself to handle and send the notification?