const char* MqttClient_GetProtocolVersionString(MqttClient *client)
{
    const char* str = NULL;
    int ver = MqttClient_GetProtocolVersion(client);
    switch (ver) {
        case MQTT_CONNECT_PROTOCOL_LEVEL_4:
            return "v3.1.1";
    #ifdef WOLFMQTT_V5
        case MQTT_CONNECT_PROTOCOL_LEVEL_5:
            return "v5";
    #endif
        default:
            break;
    }
    return str;
}