BG96 connect MQTT : Fail to parse domain name

I am working with bg96 communicating with MQTT. When I use GSM network to connect to MQTT it works fine. But when switching to NBIOT network, it leads to “Fail to parse domain name” error. Has anyone encountered this error? Below is my program.

AT+COPS=0,0,“Viettel”,9

OK

AT+QICSGP=1,1,“nbiot”,"","",1

OK

AT+QIACT=1

OK

AT+COPS?

+COPS: 0,0,“Viettel Viettel”,9

OK

AT+QMTOPEN=0,“http://tailor.cloudmqtt.com”,12269

+QMTOPEN: 0,4

Mqtt is application protocol , it is not related with GSM or nBiot , so this fault caused by low network rate and network overhead .

for example ,do not connect AWS from china mainland via NBiot