Saya menuliskan nomor rekening di kertas kecil supaya tidak salah saat transfer.

Menuliskan is from the base verb tulis with the affixes meN- and -kan.

In this sentence, menuliskan nomor rekening means to write down the account number. It often sounds a bit more deliberate or purposeful than just menulis.

• menulis = to write
• menuliskan = to write something down / to write something out

So:

• Saya menulis nomor rekening = I write the account number
• Saya menuliskan nomor rekening = I write down the account number

Both can work here, but menuliskan fits nicely because the speaker is writing the number down for later use.

Nomor rekening means bank account number.

• nomor = number
• rekening = account, usually a bank account in this kind of context

So nomor rekening is the number used to identify a bank account.

A learner should know that rekening can sometimes also refer to a bill/check/tab in other contexts, but here it clearly means a bank account.

Yes. In Indonesian, di is a very general preposition that can mean in, at, or on, depending on context.

So di kertas kecil means:

• on a small piece of paper
• literally, something like on small paper

English uses different prepositions very precisely, but Indonesian often uses di in all these situations.

In natural English, you would usually translate kertas kecil here as a small piece of paper.

Literally:

• kertas = paper
• kecil = small

So word-for-word it looks like small paper, but the natural idea is a small piece/sheet of paper.

If someone wanted to sound a little more specific in Indonesian, they might say something like:

• selembar kertas kecil = a small sheet of paper

But di kertas kecil is understandable and natural enough.

Supaya means so that or in order that.

In this sentence:

• supaya tidak salah = so that I won’t make a mistake

Yes, supaya is very similar to agar. In many cases, they can be used interchangeably.

For example:

• Saya menuliskan nomor rekening supaya tidak salah.
• Saya menuliskan nomor rekening agar tidak salah.

Both mean basically the same thing.

Supaya is very common in everyday speech.

Because tidak salah describes not being wrong / not making a mistake, while jangan salah is a command meaning don’t be wrong or don’t make a mistake.

Here the sentence is expressing a purpose:

• I wrote it down so that I wouldn’t make a mistake

That is why tidak salah is correct.

Compare:

• supaya tidak salah = so as not to make a mistake
• jangan salah = don’t make a mistake

The second one would sound like an instruction to someone.

Here salah means something like to be wrong or to make a mistake.

In context, supaya tidak salah saat transfer means:

• so I don’t make a mistake when transferring
• so I don’t enter the wrong number during the transfer

Indonesian often uses salah in a broad way. It does not always need a direct object.

For example:

• Saya salah. = I’m wrong.
• Jangan sampai salah. = Don’t make a mistake.
• Dia salah tulis. = He/She wrote it incorrectly.

So in this sentence, the exact mistake is understood from context.

Saat transfer means when transferring or during the transfer.

• saat = when / at the time of / during
• transfer = transfer, especially a bank transfer here

Transfer is a borrowed word from English, and in Indonesian it is commonly used in banking contexts. It can behave a bit flexibly, almost like a noun or an event label.

So saat transfer is a very natural short way to say:

• when making the transfer
• during the bank transfer process

A more explicit version could be:

• saat melakukan transfer = when carrying out the transfer

But the shorter form in the original sentence is very common.

The subject is understood to be the same as the first clause: saya.

So the full idea is:

• Saya menuliskan nomor rekening ... supaya saya tidak salah saat transfer.

But Indonesian often leaves out repeated subjects when they are already clear from context.

That is very normal and natural.

So even though the second saya is omitted, the meaning is still:

• I wrote down the account number on a small piece of paper so that I wouldn’t make a mistake during the transfer.

Yes, the word order is natural.

The structure is:

• Saya = subject
• menuliskan = verb
• nomor rekening = object
• di kertas kecil = place/location
• supaya tidak salah saat transfer = purpose clause

A very natural alternative order would also be:

• Saya menuliskan nomor rekening supaya tidak salah saat transfer.
• Saya menuliskan nomor rekening di kertas kecil agar tidak salah saat transfer.

You could also move the purpose phrase earlier or later depending on emphasis, but the original sentence is perfectly fine.

It could, yes.

Mencatat means to note down or to jot down, and it is very commonly used when you write information down for later reference.

So this version is also very natural:

• Saya mencatat nomor rekening di kertas kecil supaya tidak salah saat transfer.

The difference is slight:

• menuliskan = write down / write out
• mencatat = note down / jot down

In this context, both work well. Mencatat may sound a little more like making a note, while menuliskan focuses more on the act of writing it.

Yes, that is a very common learner issue.

In Indonesian:

• di as a preposition means in / at / on and is written separately
  
  • di kertas
• di- as a passive verb prefix is attached to the verb
  
  • ditulis = written

So in this sentence:

• di kertas kecil = on a small piece of paper

This is definitely the preposition di, so it must be written separately.

That spelling difference is very important in Indonesian.