I'm new here, and I just write my experience.

I have $125 e-cert for broken bathroom in the C cabin during international flight last June, and it did not work on the website as well as another did not work which was issued last December for international C lighting problem.

I called UA reservation, and right after I told my e-cert number and choice of the flight, the line cutoff.

So I gave up and buy the ticket without discount online.

(I do not imply that reservation agent cut the line... maybe because of my AT&T cellphone line)

It really sucks for customers to take such an effort to redeem inconvenient experiences.