(simple) campaign not sending mail after new user has been added

Your software
My Mautic version is: 4.0.0
My PHP version is: 7.4.23
My Database type and version is: 5.5.68-MariaDB

Your problem
My problem is:
A very simple campaign which should sent an email after a new record has been added does not sent mail.

New records are added through the API by our Wordpress website. This works fine:

These errors are showing in the log:
No errors, the log is totally empty

Steps I have tried to fix the problem:
Completely reinstalled Mautic, created the API connection again (and again), tested and cannot solve this minor issue.

Check yourmautic/var/spool directory. If your messages are spooled there via queue refer to this

Thank you for answering my question…
The var/spool directory is empty. It looks like the campaign is not triggering the email set to be send…

It has been solved! It was not sending mail due to missing cronjobs set…