connection problems for sending newsletters

Hello, since the beginning of the year I have been having problems sending the newsletters of my wordpress site lachipper.com
Mailpoet sending is set and I have deleted all invalid email addresses, but it doesn’t work.
Furthermore, when I try to preview the text, it refers me to the homepage of my site instead of the text of the newsletter.This could be related to an incompatibility with the MailPoet Task Scheduler and Siteground.
I have already activated the crontab on Siteground and their support says that their settings are all correct as requested by the plugin, but it doesn’t work anyway!At this point, since there is no solution for the problem related to the free version, I just have to uninstall and choose another solution? Or could I try to solve it in another way?

The page I need help with: [log in to see the link]