TC51 Cannot discovery Bluetooth printer ZQ320 pls Help

my TC51 using Android API 26

1. I already added AndroidManifest.xml

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.BLUETOOTH"/>

2. also added code to my activity

try {

  System.out.println("Looking for Printer");
   BluetoothDiscoverer.findPrinters(BluetoothDiscovery.this, new DiscoveryHandler() {

   @Override
   public void foundPrinter(DiscoveredPrinter discoveredPrinter) {

  System.out.println("Found Printer");
   }

   @Override
   public void discoveryFinished() {

  System.out.println("Done Find");
   }

   @Override
   public void discoveryError(String s) {

  System.out.println("Error Printer "+s);
   }

  });
} catch (ConnectionException e) {

  System.out.println(e.getMessage());
}

Callback work only discoveryFinished

Cannot find any printer. What else i have to do? i missed something?

ps. I test with ZebraDemo and it works

Thank you