I have a flight credit from a cancelled reservation (SFO - New Zealand) that are valid until May 2026. I'm trying to use the credit to book a new flight to Europe, for the same two people on the cancelled reservation, but always got the error "this credit cannot be used on the website or app, please contact customer support".

Several phone agent were not able to explain why I can't use the credit online. One of them told me this is because of certain restrictions in the original fare rule which are typical for NZ flights. But that doesn't make sense because even if I try to book a new flight to NZ, I still can't use the credit online.

While it appears the phone agent can help me apply the credit over the phone, the problem is that they can't see or use the corporate discount that I can when booking online. It's not a huge amount (~5%) but am I just out of luck here?