使用SIM7080G通过MQTTS连接AWS IoT失败的技术求助

我在用SIMCom 7080G通过MQTTS连接AWS IoT时遇到问题，正遵循《SIM7080_Series_MQTT(S)_Application_Note_V1.01.pdf》手册的5.2节配置MQTTS功能。

已成功建立NB-IoT网络连接，执行AT+CNACT?返回如下：

AT+CNACT?
+CNACT: 0,1,"10.110.7.XXX"
+CNACT: 1,0,"0.0.0.0"
+CNACT: 2,0,"0.0.0.0"
+CNACT: 3,0,"0.0.0.0"
OK

后续发送以下AT命令均返回OK，但AT+SMCONN命令执行失败：

AT+CFSINIT
AT+CFSWFILE=3,"ca.crt",0,1168,5000           (-> 此处上传从AWS下载的AmazonRootCa1.pem)
AT+CFSWFILE=3,"myclient.crt",0,1204,5000     (-> 此处上传从AWS下载的xxx-certificate.pem.crt文件)
AT+CFSWFILE=3,"myclient.key",0,1652,5000     (-> 此处上传从AWS下载的xxx-private.pem.key文件)
AT+CFSTERM
 
AT+SMCONF=URL,xxx.iot.eu-central-1.amazonaws.com,8883
AT+SMCONF=KEEPTIME,600
AT+SMCONF="CLIENTID","pico1"
At+CSSLCFG="SSLVERSION",0,3
AT+CSSLCFG="CONVERT",2,"ca.crt"
AT+CSSLCFG="CONVERT",1,"myclient.crt","myclient.key"
AT+SMSSL=1,"ca.crt","myclient.crt"
AT+SMCONN

请问我哪里操作有误？遗漏了什么配置步骤？

内容的提问来源于stack exchange，提问作者mrks