Hello Bruno.

If you set the "Default Appointment Status" to be "Approved", it should be.

Please provide me a temporary WP-admin login for your site where this happens, so we could log in and take a look ‘from the inside’ as that’s the most efficient way to see and resolve the issue. We do not interfere with any data or anything else except for the plugin (in case that’s a production version of the site), and of course we do not provide login data to third party. You can write credentials here just check Private Reply so nobody can see them except us.

Hello Bruno.

The issue here is that you have minimum capacity set to "12":

So, even though you configured the default status of appointments to be "Approved", the appointment is not complete until all 12 slots are reserved. Thus, the plugin is approving the appointment only when it is full.

Also, I booked one appointment (deleted it later) to see if the notifications send out cancellation url in the e-mail, and they do:

There's the cancellation URL in the e-mail.