Originally Posted by
headingwest
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Here is one useful thing that I discovered about the 'promotional code' field. On the website 'Book a flight' page, there is no such field on the multi-flight (more options tab). So if you have a open-jaw booking, it is not possible to redeem the voucher. Luckily, the field exists on the app, so it is possible to make a multi-flight booking there.
Unfortunately, with voucher or without it, neither on the website nor with the app mult-city booking is possible. I get an error.