Booking System and Register Button Configurations in MEC plugin can be done by going to the WordPress dashboard and change the button setting. This plugin has extensive capacity for customization in the booking. You may do this in the edit event section.
Here we can see a conversation from the Modern Events Calendar’s support desk which is about Booking System

MEC User
Hi,
Register button is not showing even if I’ve set ticket limits in the event.
Please assist.
Thanks,
Hello,
Firstly, please look at your MEC single event edit page. The event should not be expired. Then go to the booking section and check the ticket, you should have a ticket for showing button, also, please go to
WordPress Dashboard > Appearance > Widgets
and check MEC Sidebar. You need to enable the register button on single event sidebar items
Finally, you need to check the payment gateway, make sure one of them is enabled.
Regards,

Support Staff

MEC User
Hello,
We would like to be able to display early bird pricing that shows up until a specified date. Is that possible?
Hi,
Yes, you can use this option (Price Per Date) in edit event page
Best Regards

Support Staff
Settings> Booking> Limitation> Limit: If this value is less than one, the user will not be able to book the event.
Settings> Booking> Interval Options> Show Booking Form Interval: You can show the booking form only at certain times before the event start. If you set this option to 30 then the booking form will open only 30 minutes before starting the event!
Event> Booking> Total Booking Limit: If this value is less than one, the user will not be able to book the event.
Event> Booking> Total User Booking Limits: If this value is less than one, the user will not be able to book the event.
Event > Booking > Ticket > limit: If this value is less than one, the user will not be able to book the event.
No Comment.