Hi,
In order to be able to use that automatic sending one needs a valid Essential or Enterprise subscription.
Assumin you have one, please go to Acymailing->Configuration->License. (if this tab is not present you're using an outdated Acymailng version). On this tab, copy your license key and unattach the license. Click save and attach your license again. Save, activate your cron and save the config again.
If this does not resolve the issue, copy the cron url and visit this url using your browser. Check if it shows errors either on screen or in the cron log that you will find in Acymailing->Configuration->Queue process.