Firstly we need to discuss WHAT a cron is, and how it affects JoomMerkating and your auto responders and Automated Tasks.
1 - What is the cron and how to add?
Well, in order for a website to send batches of emails, or run certain processes continually, something must 'call' the site in order to tell it to check/run certain commands. In JoomMarketing, this 'CRON' call checks the email queue and automations to see if there is any emails to send, or automated tasks to run.
You need to log into your hosting control panel, and setup your OWN cron for JoomMarketing. This is usually a good option when you want to increase the number of times or frequency that JoomMarketing is able to run Tasks or send batches of emails, for a more in depth step by step on adding crons in Cpanel Hosts: https://www.siteground.com/tutorials/cpanel/cron_jobs.htm
2 - Cron command to run
wget http://YOURDOMAIN.com/index.php?option=com_joommarketing&view=cron -O /dev/null
3 - Quick check
To check your cron URL, you can goto http://YOURDOMAIN.com/index.php?option=com_joommarketing&view=cron in your browser and you should see a success message similar to:
{"success":true,"message":null,"messages":null,"data":["true"]}