The Cronjobs link displayed in the Notification in the Appointment Reminder Next day isn't correct. When adding this to the Cronjobs option in the DirectAdmin of our domain an error popped up. When I asked the hosting provider about the error message I got the message that your Cronjob displayed isn't correct.

They replied I am not the first customer that has this issue. They replied the rootcause is WP-Amelia. The manual of Cronjobs isn't correct. An URL by itself isn't a command. The Cronjob command should be one of the following commands:

curl -sL "https://www.bellyprint.nl/wp-admin/admin-ajax.php?action=wpamelia_api&call=/notifications/scheduled/send" >/dev/null
wget -qO - "https://www.bellyprint.nl/wp-admin/admin-ajax.php?action=wpamelia_api&call=/notifications/scheduled/send" >/dev/null
/opt/alt/php81/usr/bin/php-cgi -qf /home/u141552p134688/domains/bellyprint.nl/public_html/wp-admin/admin-ajax.php action=wpamelia_api call=/notifications/scheduled/send >/dev/null

The php-cgi command should be the most effective, because it doesn't run via Paache, howeer with wget as php-cgi I don't get any output. So a guarantee it works like this cannot be given. They advise to go for a curl command:

curl -sL "https://www.bellyprint.nl/wp-admin/admin-ajax.php?action=wpamelia_api&call=/notifications/scheduled/send" >/dev/null

The timing can be managed by the  */15 bij minutes setting and leave the other fields input with  * . In this way it works. 

I suggest to delete the link you display in the UI of the Notifcation Appointment Reminder Next day