Без предоплаты бронь не действует.

Because без always requires the genitive case.

• предоплата = prepayment, advance payment
• Genitive singular: предоплаты

So:

• без предоплаты = without prepayment

This is a very common pattern in Russian:

• без сахара = without sugar
• без воды = without water
• без паспорта = without a passport

So the grammar here is completely regular.

Предоплата means prepayment, advance payment, or sometimes a deposit paid in advance.

It is built from:

• пред- = before, in advance
• оплата = payment

So предоплата is money paid before the full service is provided.

Depending on context, English translations could be:

• prepayment
• advance payment
• deposit

But the exact English wording depends on the business situation.

Бронь means booking or reservation.

It is very common in everyday Russian, especially in hotels, travel, restaurants, and services. It is a shorter, more conversational word related to бронирование.

A useful distinction:

• бронь = the reservation itself
• бронирование = the act/process of booking, or a more formal word for reservation

So in signs, notices, and casual business language, бронь is extremely natural.

Literally, действует means acts, operates, or is in effect.

In this sentence, it means something like:

• is valid
• takes effect
• applies
• is active

So бронь не действует means the reservation is not valid or does not take effect.

This is a very common Russian way to talk about rules, offers, tickets, reservations, and documents:

• Скидка не действует = The discount is not valid / does not apply
• Билет действует до пятницы = The ticket is valid until Friday

Because Russian normally omits the present-tense form of to be.

In English, you say:

• The reservation is not valid

In Russian, you usually just say:

• Бронь не действует

There is no present-tense есть used here. That is normal Russian grammar.

So the sentence is not missing anything; it is complete as it is.

Because the subject is бронь, which is singular.

• бронь = one reservation / reservation as a general concept
• действует = it is valid / it applies

Russian verbs agree with the subject in number:

• Бронь действует = The reservation is valid
• Брони действуют = The reservations are valid

Here the sign is using singular бронь in a general, rule-like sense.

Yes, бронь is feminine.

Many Russian nouns ending in -ь can be either masculine or feminine, so you often have to learn their gender individually. Бронь is feminine.

You can see that from forms like:

• nominative: бронь
• genitive: брони

And from agreement in other contexts, for example:

• моя бронь = my reservation
• новая бронь = a new reservation

Even though this sentence does not show an adjective or past-tense verb, the noun itself is feminine.

Yes, that would also be correct.

Compare:

• Без предоплаты бронь не действует.
• Бронь без предоплаты не действует.

Both mean essentially the same thing. The difference is mostly word order and emphasis.

• Без предоплаты first: emphasizes the condition without prepayment
• Бронь first: starts with the topic the reservation

Putting Без предоплаты first sounds very natural for a rule or notice, because it highlights the requirement right away.

Usually it means reservations in general.

Russian often uses the singular in notices, rules, and general statements:

• Билет возврату не подлежит = Tickets are non-refundable / This ticket is non-refundable
• Маска обязательна = A mask is required / Masks are required

So бронь here is singular in form, but it expresses a general policy:

A reservation is not valid without prepayment.

Yes. For example:

• Бронь без предоплаты недействительна.

That means The reservation is invalid without prepayment.

The difference is mostly stylistic:

• не действует = very common, practical, everyday wording
• недействительна = a bit more formal, official, or legal-sounding

In a hotel or booking context, не действует sounds very natural.

Yes, there can be.

• предоплата = prepayment in general
• аванс = advance payment, often specifically a partial payment made beforehand

In some situations they can overlap, but they are not always identical.

If a business says:

• Без предоплаты бронь не действует

it means some kind of payment must be made in advance. That payment might be a full prepayment or just a required deposit, depending on the policy.

So learners should not assume that предоплата always means 100% of the price. Context matters.

A fairly literal translation would be:

Without prepayment, the reservation does not take effect.

Or even more literally:

Without prepayment, the booking does not operate.

That is why natural English usually translates it as:

• A reservation is not valid without prepayment
• Without prepayment, the booking is not valid

The main stresses are:

• без предопла́ты бронь не де́йствует

Word by word:

• предопла́та
• бронь
• де́йствовать / де́йствует

Stress is important in Russian pronunciation, so it is worth learning the stressed syllables together with the word.