Cant send mails with ver. 3 (but with ver 1 and 2 I could)

Running MailPoet ver 3 on latest WP version on https://www.fleksjobbernetvaerket.dk

History: I come from version 1, tried version 2, and now I’m version 3 – since yesterday.

Issue: I can send test mails and receive them. But I cannot send to my 400 receivers. Theres no progress. Its just “silent”.

I dont know where to look for errors.

The system says:
For the plugin to work, it must be able to establish connection with the task scheduler.
Task Scheduler
https://www.fleksjobbernetvaerket.dk?mailpoet_router&endpoint=cron_daemon&action=ping
Connection unsuccessful. Please consult our knowledge base article for troubleshooting tips.