The Install URL (which can either be a link or a QR code) is what links a device to its designated location. It needs to be opened on your chosen Android device with the In-Store Merchant App already installed.
The reason why you see this error may be because:
Your chosen Android Device does not have the In-Store Merchant App installed yet.
The good news is that it’s easy to install the In-Store Merchant App! Simply download it from the Google Play Store using this link.
ℹ️ Read more on Setting Up the In-Store Merchant App.
More on Setting Up