You can add credits to users. To add the credits, go to "members" and search for the member. On the client card select "add credits". system will scroll down to "credits" section. "expand" button will be shown if you've the permission. Click on "expand" and then click on "add new credit". Enter amount and select expiry date, then press "save". Credits are now added to your account. You can reserve a spot using these credits.
1 credit in the system is equal to 1SEK or 1USD depending on your market.