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.