Is anyone else copying the pronunciation of numbers exactly, yet the feedback says you're wrong? Every non-number I speak turns green while every number word (except thousand or million) turns red. I swear I have copied the example pronunciation phoneme for phoneme.
I think двістa is an old form still used in some diasporas.
Maybe двісті is a Russian influence. In does not truly make much sense that Russian has двести/триста/четыреста either: it comes from the time when the languages still had the dual number , so сто-сті-ста-сот would all be legitimate forms used with numerals.