Клиент уверяет меня, что платёж отправлен.

A word-by-word breakdown:

• Клиент = the client / customer
• уверяет = assures, insists, keeps saying
• меня = me
• что = that
• платёж = payment
• отправлен = sent

So the structure is literally:

Client assures me that payment sent

In natural English, that becomes:

The client assures me that the payment has been sent
or
The client insists that the payment was sent

The exact English wording depends on context.

Because the verb уверять normally takes a direct object in the accusative case:

• уверять кого? = to assure whom?

So:

• уверяет меня = assures me
• уверяет клиента = assures the client
• уверяет нас = assures us

This is different from some English patterns where learners may expect something like to say to me. In Russian, уверять works more like to assure someone, so the person being assured is in the accusative.

Уверяет is the present tense of the imperfective verb уверять.

Here it means something like:

• is assuring
• keeps assuring
• insists

This often suggests an ongoing situation: the client is currently saying this, or has been saying it repeatedly.

Compare:

• уверяет = is assuring / keeps insisting
• уверил = assured once, completed in the past
• уверит = will assure

So in this sentence, уверяет fits well if the speaker is describing the client’s current claim.

It can suggest either, depending on context.

Уверять often means:

• to assure
• to insist
• to keep saying confidently

So Клиент уверяет меня... could mean:

• The client assures me...
• The client insists...

If the speaker trusts the client, assures may sound better.
If the speaker is doubtful or slightly skeptical, insists may fit better.

Russian often leaves that nuance to context.

Что introduces a subordinate clause, like that in English:

• Клиент уверяет меня, что...
• The client assures me that...

Everything after что is the content of what the client is saying.

So:

• Клиент уверяет меня = the main clause
• что платёж отправлен = what the client claims

In everyday English, that is often omitted, but in Russian что is normally kept here.

Because отправлен is a short passive participle, not a normal past-tense verb.

• отправил = sent in the sense of someone sent it
• отправлен = has been sent / is sent

So:

• платёж отправил would mean the payment sent..., which does not make sense because the payment is not the sender.
• платёж отправлен means the payment has been sent

This is a very common Russian way to talk about completed results, especially in formal or business language.

Отправлен is the short-form passive past participle of отправить.

That sounds technical, but the important idea is simple:

It describes the result of an action done to something.

• отправить = to send
• отправлен = sent / has been sent

It agrees with платёж, which is masculine singular.

Compare the forms:

• masculine: отправлен
• feminine: отправлена
• neuter: отправлено
• plural: отправлены

Examples:

• Посылка отправлена. = The parcel has been sent.
• Письмо отправлено. = The letter has been sent.
• Документы отправлены. = The documents have been sent.

Because платёж is the grammatical subject of the clause платёж отправлен.

In that clause, the structure is basically:

• payment
  • is sent / has been sent

So платёж stays in the nominative because it is the thing being described.

Even though in meaning it is the thing affected by the action, Russian passive-style constructions like this still use the nominative for the subject:

• Заказ оформлен. = The order has been processed
• Счёт оплачен. = The invoice has been paid
• Платёж отправлен. = The payment has been sent

Yes. Платёж был отправлен is also correct.

Difference:

• платёж отправлен = more compact, often focuses on the current result: the payment has been sent
• платёж был отправлен = explicitly past, often more narrative or formal: the payment was sent

In business Russian, the version without был is very common.

So:

• Платёж отправлен = normal, concise
• Платёж был отправлен = also fine, but a little heavier

Yes, they are the same word.

The letter ё is often written as е in everyday Russian writing, so you may see:

• платёж
• платеж

Both represent the same word: payment.

However, ё shows the correct pronunciation and stress more clearly:

• платёж = stress on the last syllable

For learners, seeing ё is helpful.

Yes, Russian word order is flexible.

The neutral order here is:

• Клиент уверяет меня, что платёж отправлен.

But other orders are possible for emphasis:

• Меня клиент уверяет, что платёж отправлен.
  Emphasis on me
• Что платёж отправлен, клиент уверяет меня.
  More literary or emphatic
• Клиент меня уверяет, что платёж отправлен.
  Also natural

Even when the word order changes, the cases and verb forms show the grammatical relationships.

For a learner, the original version is the most neutral and useful pattern.

Yes, it sounds fairly neutral-to-formal, and very natural in business or customer-service contexts.

Two things make it sound especially suitable for that setting:

• клиент = client/customer
• платёж отправлен = a standard business-style way to say payment has been sent

In casual conversation, people might also say something less formal depending on the situation, but this sentence is perfectly normal for work, finance, support, or accounting contexts.

Grammatically, that is possible, but in natural English it is usually better to say:

• the payment has been sent
• the payment was sent

Russian short passive forms like отправлен often correspond to English has been sent when the result matters now.

So in this sentence, the most natural translation is usually:

The client assures me that the payment has been sent.

That captures the sense better than is sent.