Questions & Answers about Kiistän pysäköintivirheen.
Kiistän is the 1st person singular form of kiistää, which means to deny, to dispute, or to contest.
In this sentence, it means that the speaker is denying or contesting the parking violation/allegation. In an official context, it can sound a bit formal, like I contest the parking violation.
Finnish often leaves out subject pronouns when they are already clear from the verb ending.
Here, kiistän ends in -n, which tells you the subject is I. So Kiistän pysäköintivirheen already means I deny the parking violation.
You could say Minä kiistän pysäköintivirheen, but that would usually add emphasis, as if you were saying I deny it.