I'm trying to print to a ZD621 label printer with BLE. Is there a way to do this without using the Link-OS SDK. I would prefer using Swift instead of Objective C.

I'm using the Swift way of connecting to the printer using Core Bluetooth with the CBCentralManager.
I get a connection using:
let PRINTER_SERVICE = CBUUID(string: "0xFE79")
However, when I query for services, I get an empty list:
central.state is .poweredOn
2021-08-04 10:22:57.403049-0400 EquipLabelPrinter[319:6039] Metal API Validation Enabled

Connected!
Services size = 0

func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
print("Connected!")

//The following call returns 0 services.
printerPeripheral.discoverServices([PRINTER_SERVICE])
}
}
extension PrinterViewController: CBPeripheralDelegate {

func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {

guard let services = peripheral.services else { return }
print("Services size = \(services.count)")
for service in services {
print(service)
peripheral.discoverCharacteristics(nil, for: service)
}
}
Any help would be appreciated!