banpumeneun jumun beonhoga piryohapnida.

에는 is 에 + 는.

• 에 can mark a context, situation, or “in/for” meaning.
• 는 adds topic or contrast.

So 반품에는 means something like:

• for returns
• when it comes to returns
• as for returns

It gives the sentence a slightly topical sense: In the case of returns, an order number is needed.

Without 는, 반품에 주문 번호가 필요합니다 is also possible, but 에는 sounds a bit more like setting up the topic or emphasizing that this requirement applies to returns.

This is a very common Korean pattern.

With 필요하다 (to be necessary / to be needed), the thing that is needed is usually marked with 이/가, not 을/를.

So:

• 주문 번호가 필요합니다 = An order number is necessary / needed

Korean treats 필요하다 more like to be necessary than to need.

A helpful way to think about it is:

• English: We need an order number
• Korean: An order number is necessary

That is why 주문 번호가 sounds natural here.

반품 means return, especially in a shopping or product context, like returning an item you bought.

Examples:

• 반품하다 = to return an item
• 반품 신청 = return request
• 반품 기간 = return period

In this sentence, 반품에는 means for returns or when making a return.

주문 번호 is a noun-noun combination:

• 주문 = order
• 번호 = number

So together it means order number.

This kind of noun combination is very common in Korean, just like in English:

• 전화 번호 = phone number
• 여권 번호 = passport number
• 예약 번호 = reservation number

필요합니다 is the formal polite style.

Dictionary form:

• 필요하다

Formal polite:

• 필요합니다

This style is very common in:

• notices
• customer service
• official writing
• instructions
• business situations

So this sentence sounds natural for a store policy, website notice, or help-center message.

Yes. Korean often leaves out the subject when it is obvious or not important.

This sentence does not explicitly say who needs the order number. The meaning is general:

• An order number is required for returns
• You need an order number for returns

Depending on context, the implied subject could be:

• you
• customers
• one
• or no specific subject at all, just a general rule

That kind of subject omission is very normal in Korean.

Very literal word-for-word, it is something like:

• 반품에는 = for returns / as for returns
• 주문 번호가 = an order number
• 필요합니다 = is necessary

So the structure is basically:

For returns, an order number is necessary.

That is why the natural English translation becomes:

• An order number is required for returns.
• You need an order number for returns.

Yes, that is a very natural translation.

The Korean sentence is a general requirement statement, so several English versions work:

• An order number is required for returns.
• You need an order number for returns.
• To return an item, you need an order number.

The Korean does not literally use a to return grammar form here, but the meaning is essentially the same.

Both can mean something very similar, but the nuance is a little different.

• 반품에는 주문 번호가 필요합니다

  • For returns, an order number is required
  • more like a general rule or policy

• 반품하려면 주문 번호가 필요합니다

  • If you want to return it / To make a return, you need an order number
  • focuses more on the action the person wants to do

So:

• 반품에는 = more category/policy-oriented
• 반품하려면 = more action-oriented

In many contexts, you need 주문 번호 because 번호 alone just means number, which is too vague.

Compare:

• 번호가 필요합니다 = A number is needed → unclear: what number?
• 주문 번호가 필요합니다 = An order number is needed → clear

If the context is already extremely obvious, people might shorten it in conversation, but in a clear written notice, 주문 번호 is much better.

Because of a few features working together:

• 반품에는 sets up a general topic
• 주문 번호가 필요합니다 uses the formal polite style
• there is no personal subject like 제가 or 당신은
• the sentence states a rule, not a personal feeling

So it sounds like something you would see in:

• an online store FAQ
• return instructions
• customer service guidance
• a store notice

In other words, it sounds objective and informational rather than conversational.