I don't believe that this is allowed, per the TVC (on the back). With my last NW certificate (non-E cert) TVC was not allowed on that back of that certificate either. However, the reservation agent didn't know this and set up the reservation with an applied credit. Before they had said no, so kept trying. Thus, got it set up and sent it in, and taken care of. Ticket by mail. I realize that this is an E-Cert, and if this entails making an electronic purchase, I don't see how. Just my limited experience.am interested in the answer.