by marva hanlon.
It seems like you're encountering an undefined constant error in the Booking plugin. To fix this, ensure the plugin is updated to the latest version, as this might be a bug resolved in an update because it is same issue as my site: https://polyphiamerchandise.shop/. If that doesn’t work, check the mod/booking/classes/dates.php file for missing constants or syntax issues. You might also want to reach out to the plugin’s support team for more detailed troubleshooting.