Use restriction:
Electronic travel certificates can be used for travel on United- and United Express®-operated flights. Any traveler can use a travel certificate, even if they weren't on the original itinera
Additional information:
Booking with a certificate
You can redeem a travel certificate for yourself and additional travelers when booking a flight on united.com or the United app.
When selecting your payment method, choose to apply a travel certificate and enter the year issued, your PIN code, and the last name on the certificate.
