Error in name or surname
According to the rules of Ukrzaliznytsia, three non-essential errors are allowed in the ticket, which will not affect the reading of the name and surname. If you did one gross error on the ticket, the conductor has the right not let you on the train. For example, your name is Nevsky, but the ticket contains Vensky. In fact, a typo is one, but it affects the reading of the data. If a minor mistake is made both in the name and in the surname, such ticket is considered valid. For example, your name is Ivanov, and ticket contains Ivonov, or Roman is your name, and ticket contains Roma.
The language on the ticket and in the document must match. This means if you give an international passport for checking the identity, the data on the ticket must be written in Latin. Data entered in the Russian or Ukrainian does not differ significantly, so this should not bother you.
Check the entered data before payment of the ticket, you will not be able to make changes after purchase.