V-Flyer

We have just qualified for a companion voucher. We are looking to book seats later this year, dates not available yet. My question is if I book a seat with points can I use the companion voucher alongside or do I have to pay for the seat then use the companion voucher. Is the easiest way to book to call Flying Club? I tried to do a search but all the answers seemed to be from people who have already used them. Thank you for any advice.