"Seventy, eighty, ninety"
Translation:Сімдесят, вісімдесят, дев'яносто
You’re using the Latin letter 'i', not the Cyrillic 'і'. Some Cyrillic and Latin letters look the same (other letters like this are a—а, e — е, ï — ї, o — о, p — р, c — с, y — у, x — х), but on computer they are encoded completely differently and most programs don't allow replacing Cyrillic letters with Latin lookalikes.
You probably use a Russian keyboard layout that doesn't include «і». You'd probably need to install Ukrainian keyboard layout, or use some program like AutoHotkey in Windows to allow you to enter і.