From Joomla4, we can't setup the Cron task command to cron.php as in previous Joomla versions. To solve this matter, we release new version of the system plugin: OS Services Booking - Cron task In this version, you can setup the Cron task command on your hosting to run the function to send reminder emails and sms to customers
By default, OS Services Booking Booking uses a system plugin to trigger sending reminder emails and SMS process. That mean it requires someone access to the site (search engine bots are also counted) to trigger process. Sometime, it is not reliable or causes multiple emails sent to administrators in case your site has a very high traffic. To address that limitation, you can setup cron job from your hosting account to trigger sending reminder notifications instead. Please see detailed instructions below:
https://domain.com/index.php?trigger_code=SECRETCODE
That will make the reminder only processed when there is a request made to that URL (which should be secret as no real users will access to that URL). It will make it more reliable compare to replying a system plugin.