AWS-IoT MQTT does not connect - Quectel EC-21

I have a Quectel EC21 Mini PCI based board.

Upon running the ATI command it says this as firmware version,
Revision: EC21EFAR06A01M4G

I am facing issues in connecting to the AWS - MQTT.

I have verified all my certificates to be correct and it works with the Python PAHO packages on my system.

But with the EC-21 after referring to the relevant MQTT application notes doing as per it always results in the AWS-IoT being not connected.

+QMTOPEN: 0,-1 error

The issue is something similar to this topic, but not sure whether any resolution was provided.

Do I need to upgrade the firmware on the EC-21 module here?

Let me know how can we resolve this issue?

  1. Check whether the module has a card recognition (AT+CPIN?)
  2. Check whether the module is registered on the network (AT+CEREG?; return 0,1 to normal network injection)
  3. Check the signal quality of the module (AT+CSQ)

Yes, I have checked all these.

The AWS-IoT endpoints are also correctly defined. I have verified the AWS-IoT with the same configurations using a Python script.