"Connect failed" when trying to connect to the DocumentDB cluster from AWS C9

In order to insert data to a cluster with a python script, I try to connect to my cluster DocumentDB on AWS from AWS C9 with this tutorial. But every time I try to connect I get connection failed after 6 attempts:

    (scr_env) me:~/environment/sephora $ mongo --ssl --host xxxxxxxxxxxxx:xxxxx --sslCAFile rds-combined-ca-bundle.pem --username username --password mypassword
    MongoDB shell version v3.6.3
    connecting to: mongodb://xxxxxxxxxxxxx:xxxxx/
    2022-03-22T23:12:38.725+0000 W NETWORK  [thread1] Failed to connect to xxx.xx.xx.xxx:xxxxx after 5000ms milliseconds, giving up.
    2022-03-22T23:12:38.726+0000 E QUERY    [thread1] Error: couldn't connect to server xxxxxxxxxxxxx:xxxxx, connection attempt failed :
    connect@src/mongo/shell/mongo.js:251:13
    @(connect):1:6
    exception: connect failed

I tried to remove the lock file to repair the instance as they do in this answer:

    (scr_env) me:~/environment/sephora $ sudo rm /var/lib/mongodb/mongod.lock
    rm: cannot remove '/var/lib/mongodb/mongod.lock': No such file or directory

I know that the "fail to connect" error can be caused by a lot of reasons, but usually they are:

• the service (mongo) might not be running on the destination server;
• the service (mongo) might be listening on a different port number;
• the service (mongo) might be protected by a firewall somewhere on the destination.

So how can I ensure that:

• mongo is running on the destination host?
• mongo is listening on the defined port?
• I've allowed to connect to the destination host on the defined port from the IP address or network range you're running the command to connect?