I completly gave up trying to use my (paid) lifelong Silver Wing membership for flights. Nobody at 'my' UA local office in Zürich knows how to accept vouchers and how to do such bookings.

And 'fighting' UA-USA from faraway Switzerland seems not being worth my time and money.

My simple solution was/is not to buy any UA flights anymore (and for some rare inner USA flights I use now miles/awards form my LH miles&more program). Well, my former 1-K membership level is a thing of the past - long live my now life long LH miles&more Senator-level (StarAlliance Gold) membership level ...