Mistakes in the first name and last name
According to the current rules of Ukrzaliznytsia, you are allowed to make up to 3 mistakes (misspells) when writing the first name and last name if these mistakes do not significantly impede the reading of the first name and last name.
If there are more errors, data are significantly distorted from the original, or the date of the train departure is specified incorrectly, you must return a train ticket and purchase a new one. Due to technical and organizational reasons, it is impossible to make changes to successfully purchased documents.
Input language error
On a railway ticket, first name and last name of a passenger must be specified in the same language in which they are specified in a document that will be shown to a train conductor. It means that if an international passport will be shown as an identity document, the first name and last name must be specified in Latin characters.
If the last name did not fit on a ticket
If your last name did not fully fit on a ticket for some reason, it is not a problem, since the par. 2.35 of the "Rules of Passenger Transportation" says that it is allowed to shorten the last name to 20 characters.