SIM7080G - unable to connect with HiveMQ

[twizzter]

Trying to connect to the HiveMQ broker (serverless option).
Documentation says that the endpoint device should have "letsencrypt.org isrgrootx1.pem" certificate installed. Modem has to support SNI as well.

AT commands below:

Code: [Select]

[isrgrootx1 uploaded to the modem via QPST]

AT+CSSLCFG="CONVERT",2,isrgrootx1.pem
AT+CSSLCFG="sslversion",1,3
AT+CSSLCFG="SNI",1,"[id here].s1.eu.hivemq.cloud"

AT+SMCONF="CLIENTID","1234"
AT+SMCONF="URL","[id here].s1.eu.hivemq.cloud",8883
AT+SMCONF="USERNAME","[userhere]"
AT+SMCONF="PASSWORD","[passhere]"
AT+CSSLCFG="sslversion",1,3
AT+SMSSL=1,"isrgrootx1.pem",""
[all commands returned OK]

AT+CNACT=0,1
OK
+APP PDP: 0,ACTIVE
AT+SMCONN
+CME ERROR: operation not allowed
Communication with the no-SSL HiveMQ broker works fine.
The date and time on the modem are set correctly.
As far as I understand, the broker does not require any additional certificates. Not sure about this detail, but Simcom MQTT tutorial mentions three files:
-ca.crt (assume this is the isrgrootx1 in my case?)
 -myclient.crt
 -myclient.key

Any Simcom magicians here?