Unable to connect using mTLS and M66 MODEM

I have a M66 MODEM with revision: M66FCR01A20BT

I followed the application note “GSM SSL application note V3.4” and know how to upload the certificates and key.

I am currently able to establish a connection to a TCP server in both TCP mode and in TLS set to no authentication (seclevel=0).

I would like to be able to connect with mutual authentication level (mTLS) so I set seclevel=2

The server I want to connect to is tcpbin.com:4244.

The tcpbin.com page provides everything the client should and I tried to do both

a) I generated the client certificate and client key with the script provded on tcpbib.com, then I downloaded the root CA and loaded it into the MODEM

To load the root CA certificate into the modem I used AT+QSECWRITE= “RAM:CA0”,,

followed by the data and I received the confirmation with the checksum

Then I loaded the client certificate into RAM:CC0 in the same way

and the key into RAM:CK0.

I finally set the files with

AT+QSSLCFG=“cacert”,0,"RAM:CA0

AT+QSSLCFG=“clientcert”,0,"RAM:CC0

AT+QSSLCFG=“clientkey”,0,"RAM:CK0

b) I tried generating a certificate and signing it with the key and root certificate provided by tcpbin.com and uploaded it along with the private key I used to generate it.

Unfortunately, none of these attempts worked.

Could you kindly help me understand where the problem lies?

Thank you

Marco