Hello Pieter,
Thanks for reaching out to us!
Registrations for The Events Calendar is a third-party plugin. It is not developed, nor maintained by us, so we cannot provide support for it. You are absolutely welcome to continue using that product, and if you need support for it you can turn to the developer here.
In the description I see this: “Optionally, you can set limits for the number of guests allowed to register per event…” so there should be a setting for this.
Our extension for collecting registrations is Event Tickets which you can also download for free. I encourage you to check it out. It does have the functionality of limiting the number of registrations for an event.
With Events Calendar PRO and Event Tickets Plus you can further extend the functionalities of The Events Calendar.
I do hope this helps and maybe we’ll see you among our users in the near future.
Is there anything else I can help you with?
Cheers,
Andras