As an admin, you can make bookings for visitors who are not regular Yoffix users without paying extra for them.
Please go to People Management and create a guest profile. It does not have to contain a real email address - you can use any dummy email as a placeholder.
Save the profile, but do not invite the user.
Now, you will be able to make bookings for this account (in the Calendar or in Spaces) so that a seat will be reserved for a guest. You can create as many guest accounts as necessary. We won't charge you for users who are not registered.