japangieneun jipyega an deureogaseo dongjeon du gaereul neoheosseo.

에 marks the place or destination, and 는 adds a topic/contrast nuance.

So 자판기에는 is not just in/into the vending machine. It feels more like:

• as for the vending machine
• in the vending machine
• when it comes to the vending machine

The 는 often suggests some contrast, even if it is mild. In this sentence, it can imply something like:

• In this vending machine, bills don’t go in
• maybe unlike coins, which do work

So 자판기에 would sound more neutral, while 자판기에는 adds a slight contrastive emphasis.

Because 들어가다 is an intransitive verb, meaning to go in / to enter.

With intransitive verbs, the thing that moves is marked as the subject, so you use 가/이:

• 지폐가 들어가다 = the bill goes in

If you used 지폐를, you would need a transitive verb such as 넣다:

• 지폐를 넣다 = to put in a bill

So the sentence is describing the bill as the thing that would not go in, not directly as the object of someone’s action.

Literally, 들어가다 means to go in, so 안 들어가다 means not go in.

In this vending machine context, that can mean:

• the bill would not physically go in
• the machine would not accept the bill
• the insertion attempt failed

So it is very natural Korean for something like a machine rejecting or not taking a bill.

It does not have to mean only a physical size problem. In everyday use, it often covers the idea of it wouldn’t take it.

Here, -아서/-어서 connects the two clauses and gives a reason/cause:

• 지폐가 안 들어가서 동전 두 개를 넣었어
• Because the bill wouldn’t go in, I put in two coins

This ending can sometimes just mean and then, but in this sentence the cause-and-result meaning is the natural one.

So the flow is:

1. bills didn’t work
2. therefore, coins were used

This is a very common transitive/intransitive pair:

• 들어가다 = to go in
• 넣다 = to put in

So:

• 지폐가 안 들어가다 = the bill doesn’t go in
• 동전 두 개를 넣다 = to put in two coins

The first part describes what happened to the bill from the bill’s point of view. The second part describes what the speaker did.

English often uses put in for both ideas, but Korean often distinguishes them more clearly.

Yes, it could, but the nuance changes a bit.

• 안 들어가서 = it didn’t go in / it wouldn’t go in
• 못 들어가서 = it couldn’t go in

In many real situations, both can work. But there is a slight difference:

• 안 simply says the action did not happen
• 못 emphasizes inability

In a vending machine sentence, 안 들어가서 sounds very natural because it often implies the machine just did not take the bill.
못 들어가서 would sound a little more like it was impossible for the bill to go in.

Because Korean numbers usually use a counter construction:

• 동전 두 개 = two coins

The usual pattern is:

• noun + number + counter

So:

• 동전 한 개
• 동전 두 개
• 사과 세 개

Using 개 is normal in everyday speech for coins. There are more specific counters in Korean, but 개 is the common, practical choice.

So 두 동전 is not the normal way to say two coins.

Because Korean often leaves out subjects when they are obvious from context.

Here, after saying the bill did not go in, the second clause naturally implies that the speaker responded by putting in two coins. So I does not need to be stated.

A full version could be:

• 나는 동전 두 개를 넣었어

But that would usually be unnecessary unless you want to emphasize I.

넣었어 is casual, non-polite past tense.

It is used with:

• friends
• close family
• people younger than you
• informal conversation

The more polite version would be:

• 넣었어요

A more formal style would be:

• 넣었습니다

So this sentence is in everyday casual speech.

Korean nouns often do not mark singular vs. plural unless needed.

So 지폐가 안 들어가서 can mean:

• the bill wouldn’t go in
• bills don’t go in
• paper money doesn’t work

The exact interpretation comes from context.

In this sentence, it could mean either:

• the speaker tried a bill and it did not go in
• the machine does not accept bills in general

Both are possible unless the larger context makes one clearer.

The version with 는 sounds more contrastive or topic-oriented.

• 자판기에 = more neutral, simply into the vending machine
• 자판기에는 = as for the vending machine / in the vending machine, at least

So 자판기에는 can subtly suggest:

• this machine, specifically, doesn’t take bills
• at least in this machine, bills don’t work
• the important point here is the vending machine situation

That extra 는 is very common in Korean when speakers want to set up the situation or imply contrast.