Недоимка указана в личном кабинете налогоплательщика.

Because it agrees with недоимка, which is a feminine singular noun.

• недоимка = feminine singular
• so the short-form participle must also be feminine singular: указана

Compare:

• долг указан — долг is masculine
• сумма указана — сумма is feminine
• значение указано — значение is neuter

So in this sentence, указана matches недоимка.

Указана is the short form of a passive past participle from the verb указать.

In this sentence, it means something like:

• is indicated
• is stated
• is listed
• is shown

So Недоимка указана... literally means The arrears/underpayment is indicated/listed...

This short-form participle is very common in official and written Russian, especially in bureaucratic, legal, and technical language.

Because в can take either:

• accusative for motion/direction: into
• prepositional for location: in

Here the meaning is location: the arrears are shown in the taxpayer’s personal account, not moving into it.

So:

• в личный кабинет = into the personal account
• в личном кабинете = in the personal account

That is why кабинет becomes кабинете, the prepositional singular form.

Because it depends on кабинет and shows possession: the taxpayer’s personal account.

The base noun is:

• налогоплательщик = taxpayer

Its genitive singular form is:

• налогоплательщика

So:

• личный кабинет налогоплательщика = the taxpayer’s personal account

This is a very common Russian structure:

• паспорт гражданина = the citizen’s passport
• номер договора = the contract number
• кабинет пользователя = the user’s account/dashboard

Literally, yes, the words mean:

• личный = personal
• кабинет = office / study / cabinet

But in modern Russian, личный кабинет very often means an online personal account, user dashboard, or account portal on a website.

So in this sentence, it refers to the taxpayer’s online account in the tax system, not a physical office.

Not exactly. Недоимка is more specific than the general word долг.

It usually refers to:

• arrears
• underpayment
• an amount that was not paid when it should have been, especially in tax or official payment contexts

So:

• долг = debt in general
• недоимка = unpaid required amount, often tax arrears or a shortfall in payment

That is why this sentence sounds official and administrative.

Yes, effectively it is.

Недоимка указана... focuses on the result:

• the arrears are listed/shown

It does not say who listed them.

Russian often uses short passive participles like this in formal writing instead of explicitly naming the agent.

An active version would be something like:

• Налоговая служба указала недоимку в личном кабинете налогоплательщика.
• The tax service listed the arrears in the taxpayer’s personal account.

But the passive version is more neutral and official.

Yes. Russian word order is flexible.

The sentence:

• Недоимка указана в личном кабинете налогоплательщика.

could also be:

• В личном кабинете налогоплательщика указана недоимка.

Both are grammatical.

The difference is mainly emphasis:

• Недоимка указана... puts недоимка first, so the sentence starts with the thing being discussed.
• В личном кабинете налогоплательщика... puts the location first, which can sound more like In the taxpayer’s account, the arrears are listed.

In official Russian, both patterns are common.

Because Russian has no articles.

So Недоимка can mean:

• the arrears
• an arrears amount
• the underpayment

Which one sounds best in English depends on context.

Russian leaves this to context, while English usually has to choose an article.

All of those can work, depending on context.

In official Russian, указать / указана often means:

• indicate
• state
• specify
• list
• sometimes show

For личный кабинет on a website, natural English often uses:

• The arrears are shown in the taxpayer’s personal account or
• The arrears are listed in the taxpayer’s online account

So while indicated is close to the Russian wording, shown or listed may sound more natural in everyday English.

It is definitely formal/administrative in style.

Clues:

• недоимка is official vocabulary
• указана in short passive form is common in bureaucratic writing
• личный кабинет налогоплательщика sounds like government website language

A less official sentence might use simpler wording, but for tax notices, legal texts, or government portals, this sentence sounds normal.

Here are the dictionary forms:

• недоимка → недоимка
• указана → указать (verb), or related full participle указанный
• в → в
• личном → личный
• кабинете → кабинет
• налогоплательщика → налогоплательщик

This can help you recognize the forms when cases and agreement change in real sentences.