How to change double-byte to single-byte?

I am trying to make on-line train reservations on JR EAST's website in English, but I keep on getting the message - "Please re-enter your first name. Your previous entry included a character that was not a single-byte English letter or number." How do I change alphabets to single-byte? Thank you.

Probably you have entered non-ASCII characters, such as accented letters.

What computer/tablet/smartphone and default input language are you using? I encountered similar issue before (I forgot which site) and resolved by switching the input language from Japanese to English (or vice versa) where the name was requested in Roma-ji (Roman alphabet).

Of course, the full-width Latin characters which may be used by some OSes when the input language is set to Japanese are not ASCII either. It should be possible, by the way, to use half-width characters without exiting the Japanese input mode.

we have been using Windows, both 7 and 10, using all Japanese keyboard input methods available, both Romanji and Kana. Also tried using iPad to simplify things, also added Japanese keyboard to the iOS, none worked. Always had problem with the first name section only. Tried online double and single byte character conversion, didn't work either, looks like this site is bugged, or at least its not terribly user friendly.

Any further suggestions welcome as we need to get the ticket online and time is running out.

Try setting your keyboard to US English and entering the characters of your name instead of trying to use a Japanese keyboard to enter Romaji.

Have you tried to type the text somewhere else (like Notepad) and then copy & paste it in the form field?