"I am Viktoria."
You're using the Latin «i» instead of the Cyrillic «і».
Some letters might look the same (like Latin A, Cyrillic А and Greek Α) but belong to different alphabets, so they are encoded differently on the computer. Most programs would be confused if you replace Latin i with Cyrillic і, or vice versa, and Duolingo is no exception.
Unfortunately, this means you can't use a Russian keyboard layout to type Ukrainian. Check the settings of your operating system or device, there should be an option to install Ukrainian keyboard layout.