Kiistän pysäköintivirheen siitä huolimatta, että maksuaika on jo alkanut.

Because kiistän already includes the subject I.

• kiistää = to deny / to dispute
• kiistän = I deny / I dispute

In Finnish, the verb ending usually tells you the subject, so the pronoun minä is often left out unless you want extra emphasis.

Kiistän is the 1st person singular present tense form of kiistää.

So:

• kiistää = to deny
• kiistän = I deny
• kiistät = you deny
• kiistää = he/she/it denies

In this sentence, it is the main verb of the whole sentence.

Because it is the object of the verb kiistän, and in an affirmative sentence like this, a singular total object often appears in the genitive-looking accusative form, which ends in -n.

So:

• base form: pysäköintivirhe
• object form here: pysäköintivirheen

The idea is that the speaker is denying the whole alleged parking violation/error, not just some undefined amount of it.

A useful comparison:

• Kiistän pysäköintivirheen. = I deny the parking violation.
• En kiistä pysäköintivirhettä. = I do not deny the parking violation.

In negative sentences, objects usually go into the partitive, which is why you would get pysäköintivirhettä there.

It is a compound noun:

• pysäköinti = parking
• virhe = mistake, error

So literally it is something like parking error. Depending on context, it may be translated more naturally as parking violation, parking offence, or similar.

Finnish uses compound words very freely, so one long word often corresponds to a whole phrase in English.

It means despite the fact that ..., even though ..., or in spite of the fact that ....

In this sentence:

• siitä huolimatta, että maksuaika on jo alkanut
• = despite the fact that the paid parking period has already started

This is a common Finnish structure for introducing a contrast.

Because huolimatta normally takes the elative case (-sta / -stä).

The pronoun se becomes:

• se = that / it
• siitä = from that / about that / despite that, depending on context

In the fixed expression siitä huolimatta, the meaning is idiomatic: despite that.

So even though the literal pieces do not map neatly into natural English, the whole phrase functions as one unit.

Because Finnish normally uses a comma between a main clause and a subordinate clause.

Here:

• main clause: Kiistän pysäköintivirheen
• subordinate clause: että maksuaika on jo alkanut

Since the phrase siitä huolimatta, että introduces that subordinate clause, the comma is standard Finnish punctuation.

Maksuaika is another compound noun:

• maksu = payment
• aika = time, period

So maksuaika means something like:

• payment period
• paid parking period
• time for which payment applies

Finnish very often combines nouns into one word where English would use two or three words.

On alkanut is the present perfect.

• alkaa = to begin / to start
• alkoi = started / began
• on alkanut = has started / has begun

So:

• maksuaika on jo alkanut
• = the payment period has already started

The present perfect connects a past event to the current situation. That fits well here, because the payment period started earlier and is now in effect.

Jo means already.

So:

• maksuaika on alkanut = the payment period has started
• maksuaika on jo alkanut = the payment period has already started

It adds the idea that this has happened earlier than some relevant point or is already true now.

Yes, a sentence with vaikka could express a similar idea, but the tone is a bit different.

For example:

• Kiistän pysäköintivirheen, vaikka maksuaika on jo alkanut.

This means roughly I deny the parking violation, even though the payment period has already started.

The original siitä huolimatta, että sounds a bit more formal or explicit, closer to despite the fact that.
Vaikka is often simpler and more conversational.

The sentence has a very natural Finnish word order:

• Kiistän pysäköintivirheen = main statement first
• siitä huolimatta, että maksuaika on jo alkanut = contrasting background information after it

Finnish word order is more flexible than English word order, but this version is straightforward and neutral.

The important thing is that the main meaning is:

1. I deny the parking violation
2. despite the fact that the payment period has already started

So the second part does not change the main action; it adds a contrast.

Not exactly.

• kiistää = to deny, dispute, contest
• kieltää = to forbid, prohibit, or sometimes to deny in certain contexts

In this sentence, kiistää is the right verb because the speaker is disputing or contesting a parking violation.

So:

• Kiistän pysäköintivirheen = I dispute/deny the parking violation

Using kieltää here would usually sound wrong or at least unnatural for this meaning.