BG95 MQTT publish "update" shadow on AWS reply with ERROR

I am using BG95 for an IoT application, with MQTT and AWS IoT Core. With my firmware I can publish on a random topic created ad hoc on AWS, I can publish on shadow $aws/things/thingName/shadow/name/shadowName/get without problems, but when I publish on shadow $aws/things/thingName/shadow/name/shadowName/update I receive always ERROR. It seems that the module doesn’t send out anything.
The command that I am using is:
AT+QMTPUBEX=0,1,1,0,"$aws/things/thingName/shadow/name/shadowName/update","{"state": {"reported": {"test":1}}}"
Where is the error? On AWS side we open the policy for this test.


A small update: if the payload was short the publishing is ok, otherwise with a long message (more or less 200 chars) the publishing fail! why?

Another update: The problem seems not in the lenght but in the fact that into the message there is a JSON array. Without array, a 245 chars message was sent without problems!