Include QR Code with {entry_url} in Notification

We need to include the Entry URL of the Form submission - So that customers can show the QR Code, Staff scan the QR Code and get directly to the submitted Form. We would use thirdparty API to achieve this: We tried to embed the following code into the Notification:

Code: img src=“{entry_url};size=100x100” alt="" title=""

It shows a QR Code in the Preview (when scanning obviously it reads: {entry_url}).
But when the notification is sent, it only shows a broken image in the Notification E-Mail.
Any ideas how to get this to work without 3rd party plugins?

Many Thanks!