Sierra BX310X - MQTT Configuration - Last Will message

I am using Sierra BX310X module as MQTT client. Firmware version - v.2.7.3

The MQTT configuration is as follows:
AT+KMQTTCFG=0,"<broker_address_here>",1883,4,“BX310X”,30,1,1,“lwt”,“lastwillmessage”,0,1,“username”,“password”

The MQTT configuration is successful if the lastwillmessage is short and having no double quotes. But for my application, I need a small JSON structure as my last will message.
Example: AT+KMQTTCFG=0,"<broker_address_here>",1883,4,“BX310X”,30,1,1,“lwt”,"<json_data(less than 100 bytes)>",0,1,“username”,“password”

If I add a JSON structure to this command, I’m getting “ERROR” as response from the sierra module.
Please let me know, how a JSON data can be set as last will message using MQTT AT commands.

Thank you.