Data write failure

[wang94]

Write data is prompt error, go to onRequestFailed callback failType = 3, what is this error, I wrote the operation is like this
IConnection.STATE_CONNECTED -> {
Log.d("测试结果","设备已连接状态")
val connection = Ble.instance.getConnection(device)
connection?.writeCharacteristic("bb", serviceUuid, characteristicUuid, "726561645F4C4544".toByteArray())//726561645F4C4544
}