4G version of gateway

I buy the 4G version Gateway. I would like to use only 4G to transfer the data.

I connect the gateway via Ethernet, and set up the APN, MCC, MNC.
And I use MQTT to transfer the data. I can subscribe the message from MQTT broker successfully when the gateway connects to the Ethernet cable. However, when I de-plug the Ethernet cable, I cannot subscribe the message from the MQTT broker. How can I just use 4G without Ethernet and Wifi to transfer data?

Please refer your email instead