godlie

Yes the price is set to 0, it also shows an empty div if the user is trying to confirm the booking.

Here you can see the RSVP Settings for this Event.

https://www.mint-lienz.at/event-sample-setting.png

I just had a look into the settings, within WP there is no cache plugin installed.

On the server itself, opcache was activated within php, deactivated it to test but did not realy change something.

i tried this one, but this does not realy change something.
maybe you can see an error here?

https://www.mint-lienz.at/rewrites.png

This was added to Settings -> Mail Templates -> Booking Pending Email

The generated link looks like:
https://www.mint-lienz.at/events/confirm/575e5846762d066cfd7c6efc29df5e9a893d8444a04d03/

You can see the site running on:
https://www.mint-lienz.at/