BLEDeviceConnection.kt

private val callback = object: BluetoothGattCallback() {

    ...

    override fun onCharacteristicWrite(
        gatt: BluetoothGatt,
        characteristic: BluetoothGattCharacteristic,
        status: Int
    ) {
        super.onCharacteristicWrite(gatt, characteristic, status)
        if (characteristic.uuid == /* the one you're looking for */) {
            Log.v("bluetooth", "Write status: $status")
        }
    }
}

@RequiresPermission(PERMISSION_BLUETOOTH_CONNECT)
fun writeCharacteristic(serviceUUID: UUID, characteristicUUID: UUID) {
    val service = gatt?.getService(serviceUUID)
    val characteristic = service?.getCharacteristic(characteristicUUID)
    
    if (characteristic != null) {
        // First write the new value to our local copy of the characteristic
        characteristic.value = "Tom".toByteArray()
        
        //...Then send the updated characteristic to the device
        val success = gatt?.writeCharacteristic(characteristic)
        
        Log.v("bluetooth", "Write status: $success")
    }
}