Hello Helen
I would not purchase the Jungfraujoch tickets in advance. What if there is bad weather, while you will end up in the clouds and have zero view? Would you still want to go, knowing you are doing the most expensive mountain trip one can do in Switzerland?
You can easily purchase the tickets a day before at the train station in Zurich, once you know what the weather will be like. Weather forecasts more than 2 days out are rarely reliable in Switzerland. You could still reserve the seats now, from the Jungfrau railways’ website. It would not mean a big loss if you decide not to go; the reservation for priority boarding is CHF 10 per pax.
https://www.jungfrau.ch/en-gb/jungfraujoch-top-of-europe/book-priority-boarding/
If you insist, then try entering the names in “all caps” instead of capitalizing the first letter only. This could fix the error.
Kind regards,
Roland