Bumping my experience. I had a flight booked one-way MIA-ANU, and changed the originating city to MCO. That resulted in an e-voucher for a fare difference of $81.50. Today I was booking my return flight ANU-MIA, and attempted to apply the voucher. I did not get the option on the website - the only "other payment" options were PayPal and Fly now, pay later. I reviewed the voucher conditions, checked here, and called the Platinum number.

As an aside, it's annoying that there is no menu choice to ticket a reservation - I finally got to an agent by saying, "change a reservation". Anyway, the agent was not able to apply the voucher. She said the system was telling her that I had to submit a paper voucher. I assured her that I had an e-voucher, and it said nothing about mailing it in. She talked with ticketing, and then the problem was exposed. Although my original flight was an international itinerary, the e-voucher could ONLY be used for another flight originating in the USA, PR, or USVI. I looked at the fine print and verified that was the case. It seems pretty strange to impose that restriction, but I guess it is a small price to pay for ending change fees. Because of delays caused by US government processing some documents, I have had to change my outbound flight several times.