Неоплату парковки указали в постановлении об административном штрафе.

Here it should be understood as the noun неоплата = non-payment / failure to pay, so it is written as one word.

• неоплату = accusative singular of неоплата
• не оплату would usually mean something contrastive like not the payment, but..., which is a different structure

A useful comparison:

• неоплата парковки = non-payment of parking
• не оплату, а квитанцию = not the payment, but the receipt

Also, learners may see неуплата in similar contexts. Both exist, but неоплата парковки is a common phrase in parking-related official language.

Because it is the direct object of the verb указали (indicated / listed / stated).

You can ask:

• указали что? — неоплату

So неоплата changes to the accusative singular:

• nominative: неоплата
• accusative: неоплату

This is very typical after transitive verbs in Russian.

Because it depends on the noun неоплата.

Russian often uses the pattern:

• noun + genitive to mean X of Y

So:

• неоплата парковки = non-payment of parking
• literally: the non-payment of the parking

You can think of it as answering the question:

• неоплата чего? — парковки

This is the same logic as:

• оплата проезда = payment for travel
• проверка документов = checking of documents
• нарушение правил = violation of rules

Not exactly. In this sentence, парковка is better understood as parking / paid parking / parking service, not the physical parking lot itself.

So неоплата парковки means:

• not paying for parking
• failure to pay the parking fee

This is very common in city/traffic/administrative language.

This is a very common Russian pattern: a 3rd person plural verb with no stated subject.

Literally it looks like:

• they indicated

But in English it is often translated more naturally as:

• it was indicated
• they listed
• it was stated

Russian uses this structure when the exact people are not important, unknown, or obvious from context.

So указали does not necessarily mean a specific group of people. It often works like an impersonal official statement.

Because указали is perfective, and here it describes a completed action: the document listed or stated this fact.

• указали = they indicated / they listed once, as a completed fact
• указывали = they were indicating / used to indicate / indicated repeatedly

Since the sentence refers to what was written in a specific document, the perfective form указали is the natural choice.

Because the preposition в here means in, and after в (in the sense of location), Russian uses the prepositional case.

So:

• постановление → в постановлении

This means:

• in the decision / in the official ruling / in the notice

The ending -ии is the normal prepositional singular ending for this noun.

Russian uses об instead of о before some vowels for easier pronunciation.

So:

• о штрафе
• but об административном штрафе

Both административном and штрафе are in the prepositional case, because the phrase depends on о/об:

• постановление о чём? — об административном штрафе

So the full phrase means:

• a decision / ruling about an administrative fine

In this context, постановление is an official legal/administrative document.

Depending on the exact system and context, it can be translated as:

• decision
• ruling
• order
• official notice

So постановление об административном штрафе is not just any note or message. It is a formal document connected with an administrative fine.

Russian word order is flexible, and the beginning of the sentence often shows what the speaker wants to highlight.

Starting with Неоплату парковки puts the focus on the thing that was listed in the document: the non-payment of parking.

A more neutral order would also be possible, for example:

• В постановлении об административном штрафе указали неоплату парковки.

Both are grammatical. The version you were given sounds a bit more official and front-loads the key issue.

It sounds official / bureaucratic / legal rather than conversational.

Clues include:

• неоплата парковки
• указали
• постановление
• административный штраф

In everyday speech, a Russian speaker might say something simpler, such as:

• В постановлении написали, что парковка не была оплачена.
• В документе указали, что парковку не оплатили.

So the original sentence is perfectly understandable, but it belongs to formal administrative language.