Demo app doesn't find any printers

[mormrod]

I've got a Zebra ZQ521
I've downloaded this demo app and it's running on my iPhone 8 device. It prompted me to allow the Bluetooth permission, which I did (and I can see from the iOS settings that Bluetooth is enabled for the app)

However, when I click "Click to discover Bluetooth Printers" the result immediately comes back with an empty array:
ZSDKRCTDevDemo[908:176613] [javascript] Discovered printers are: [

]

Please assist as I cannot see why it doesn't even appear to attempt to discover any devices, and why the printer wouldn't be found.

I have been able to download the Zebra Printer Setup app and successfully connected to the printer with that, so there's no issue with the printer and it's Bluetooth connectivity.

[mormrod]

EDIT: The demo app I am trying to use is the ZSDKRCTDevDemo

[ssizebra]

For running the demo on a iOS device, you need manually pairing the printer with the iPhone first through the Bluetooth settings on the phone. This is required specifically by Apple, as it doesn't allow 3rd party apps to search for the Bluetooth Classic. The discovery button on the demo simply lists out the paired and connected printers.