Exception while decoding PUBACK: fixed header flags must be 0 but were 8 – HiveMQ Client Library

admin

Hi,
The server runs on wss.certigo.com:443

I can connect to this server using org.eclipse.paho.client.mqttv3.MqttClient

I want to migrate to hivemq client library.

I receive this log when connect to the server wss.certigo.com:443

2026-04-14 13:01:54.365| DEBUG | com.hivemq.client.mqtt-1-1 | c.h.c.i.s.i.n.h.ssl.JdkSslContext – Default protocols (JDK): [TLSv1.3, TLSv1.2]2026-04-14 13:01:54.365| DEBUG | com.hivemq.client.mqtt-1-1 | c.h.c.i.s.i.n.h.ssl.JdkSslContext – Default cipher suites (JDK): [TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA, TLS_AES_128_GCM_SHA256, TLS_AES_256_GCM_SHA384]

2026-04-14 13:01:54.631| DEBUG | com.hivemq.client.mqtt-1-1 | c.h.c.i.s.io.netty.util.Recycler – -Dio.netty.recycler.maxCapacityPerThread: 4096

2026-04-14 13:01:54.631| DEBUG | com.hivemq.client.mqtt-1-1 | c.h.c.i.s.io.netty.util.Recycler – -Dio.netty.recycler.ratio: 820

26-04-14 13:01:54.631| DEBUG | com.hivemq.client.mqtt-1-1 | c.h.c.i.s.io.netty.util.Recycler – -Dio.netty.recycler.chunkSize: 32

2026-04-14 13:01:54.631| DEBUG | com.hivemq.client.mqtt-1-1 | c.h.c.i.s.io.netty.util.Recycler – -Dio.netty.recycler.blocking: false

2026-04-14 13:01:54.631| DEBUG | com.hivemq.client.mqtt-1-1 | c.h.c.i.s.io.netty.util.Recycler – -Dio.netty.recycler.batchFastThreadLocalOnly: true

2026-04-14 13:01:54.794| DEBUG | com.hivemq.client.mqtt-1-1 | c.h.c.i.s.i.n.handler.ssl.SslHandler – [id: 0x0af5cccc, L:/192.168.0.194:55096 – R:wss.certigo.com/208.95.250.117:443] HANDSHAKEN: protocol:TLSv1.3 cipher suite:TLS_AES_256_GCM_SHA384

2026-04-14 13:01:54.924| ERROR | RxComputationThreadPool-1 | ironbeamAPI.xAPI – accept errorcom.hivemq.client.mqtt.mqtt3.exceptions.Mqtt3DisconnectException: Exception while decoding PUBACK: fixed header flags must be 0 but were 8

Caused by: com.hivemq.client.mqtt.exceptions.MqttDecodeException: Exception while decoding PUBACK: fixed header flags must be 0 but were 8

2026-04-14 13:01:54.930| DEBUG | com.hivemq.client.mqtt-1-1 | c.h.c.i.s.i.n.buffer.PoolThreadCache – Freed 15 thread-local buffer(s) from thread: com.hivemq.client.mqtt-1-1

mqtt cli client also cannot connect.mqtt test -h wss.certigo.com -p 443 -V 3

MQTT 3: Could not connect MQTT 3 client – Exception while decoding CONNECT: must not receive this packet type

https://www.hivemq.com/demos/websocket-client/ can connect to wss.certigo.com:443 and returns a relevant error

Connect failed: AMQJS0006E Bad Connack return code:2 Connection Refused: identifier rejected.

This is an expected behavior using the default ClientID

How can I connect to wss.certigo.com:443 using hivemq client library?

Regards,

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