Qucetel ec200 failed to open network error

When I establish TCP connection and connect to the remote server by using MQTT protocol I faced error like failed to open network error with MQTT server my error code is +QMTOPEN: 0,-1 this code is returned a lot of time please help me?

Please check whether the MQTT domain name and port are correct, whether the server is available, whether the module is successfully connected to the network, and whether the pdp scene is activated.