QOS2 doesn't work about mqtt HOT 1 CLOSED

#include <MQTT.h>
void callback(char* topic, byte* payload, unsigned int length);

MQTT client("www.hirotakaster.com", 1883, callback);
uint16_t qos2messageid = 0;
bool qos2message = false;

// recieve message
void callback(char* topic, byte* payload, unsigned int length) {
    delay(1000);
}

// QOS ack callback.
// if application use QOS1 or QOS2, MQTT server sendback ack message id.
void qoscallback(unsigned int messageid) {
    Serial.print("Ack Message Id:");
    Serial.println(messageid);

    if (messageid == qos2messageid) {
        Serial.println("Release QoS2 Message");
        client.publishRelease(qos2messageid);
        qos2message = true;
    }
}

void setup() {
    Serial.begin(9600);
    RGB.control(true);
    
    client.connect("sparkclient");

    // add qos callback. If don't add qoscallback, ACK message from MQTT server is ignored.
    client.addQosCallback(qoscallback);

    if (client.isConnected()) {
        uint16_t messageid;
        qos2message = true;
    }
}

void loop() {
    if (client.isConnected()) {
        uint16_t messageid;
        client.loop();

        if (qos2message) {
            // QOS=2
            client.publish("outTopic/message", "hello world QOS2", MQTT::QOS2, &messageid);
            Serial.println(messageid);

            // save QoS2 message id as global parameter.
            qos2messageid = messageid;
            qos2message = false;
        }
    }
}