ProperModulation

I have a buddy who has a NJ FID. His father has a few old Garand rifles but his father does not have a FID. Can they just use a COE to do the transfer? The reason I ask is because the COD form asks for the "Transferor’s Firearms I.D. Card Number"

I have not bough anything online before. But with the severely limited stock most shops have, its looking like the best alternative. My question is the process or sequence of events. Do I need to talk to the FFL dealer in NJ FIRST and then make the purchase or do I purchase first and then have the seller contact the FFL? Sorry if this is a dumb question.