MQTT handleMessage Function Not Invoked Despite Subscription

I'm working on a Go application that subscribes to an MQTT topic and processes incoming messages using a handleMessage function. However, I'm encountering an issue where the handleMessage function is not being invoked despite the MQTT client successfully subscribing to the topic and receiving messages.

Here's a summary of the relevant code snippet:

if token := client.Subscribe(topic, 0, func(client mqtt.Client, msg mqtt.Message) {
    // Pass db as a parameter to handleMessage function
    handleMessage(client, msg, db)
    log.Printf("Received message on topic %s: %s\n", msg.Topic(), msg.Payload())
}); token.Wait() && token.Error() != nil {
    log.Printf("Error subscribing to MQTT topic %s: %v\n", topic, token.Error())
    return fmt.Errorf("failed to subscribe to MQTT topic %s: %w", topic, token.Error())
} else {
    log.Printf("Subscribed to MQTT topic: %s\n", topic)
}

// Definition of the handleMessage function
func handleMessage(client mqtt.Client, msg mqtt.Message, db *pg.DB) {
    // Logic to handle incoming MQTT messages
    // This function should be invoked when a message is received
    log.Printf("Handling MQTT message: %s\n", msg.Payload())
    // Additional processing logic...
}

Despite proper MQTT client initialization, subscription, and connection to the broker, the handleMessage function is not being invoked when messages are received on the subscribed topic. I have verified that messages are indeed being published to the topic.

Here are the steps I've taken to troubleshoot the issue:

Verified MQTT message reception and subscription parameters. Checked the connection status of the MQTT client and ensured there are no connection errors. Reviewed the implementation of the handleMessage function to ensure it's correctly defined and exported. Despite these efforts, I haven't been able to identify the root cause of the issue. Any insights or suggestions on what might be causing the handleMessage function not to be invoked would be greatly appreciated.

Thank you in advance for your assistance!

I had forgotten to remove defer client.Unsubscribe(topic) from my code. It is fixed now.