Learn Hardcore Indonesian: Saya membayar tagihan itu lewat transfer ke rekening bank. - I pay that bill by transferring to a bank account.

Indonesian verbs don’t change for tense. Saya membayar tagihan itu… can mean past, present, or future depending on context. Add time/aspect words to be explicit:

Past/completed: Saya sudah/telah membayar…; Saya baru saja/barusan membayar…
Present/progressive: Saya sedang membayar…
Future/intention: Saya akan/maи membayar…

Why is it membayar and not just bayar? Are both correct?

Both are correct. Membayar (with the prefix meN-) is more formal/standard and clearly transitive. In everyday speech, people often use the bare form: Saya bayar tagihan itu…. When the object is fronted, the prefix is normally dropped: Tagihan itu saya bayar… (still perfectly standard).

What does the prefix mem- in membayar do?

It’s the active transitive prefix meN-, which signals a verb that typically takes an object. It assimilates to mem- before a root beginning with b (so meN- + bayar → membayar). Functionally, it marks an active subject doing the action to an object.

What’s the difference between membayar, membayarkan, and colloquial bayarin?

Membayar [obj]: pay the thing itself. Example: membayar tagihan.
Membayarkan [obj] (untuk/kepada [beneficiary]): pay something on someone’s behalf or cause a payment. Example: Saya membayarkan tagihan itu untuk adik saya.
Bayarin (informal): pay for (someone/something). Example: Tolong bayarin aku = please pay for me.

What exactly does tagihan mean, and how is it different from rekening?

Tagihan = a bill/invoice (what you must pay). Rekening = a bank account. Note: in some collocations like rekening listrik (electric bill), rekening can also mean a bill/statement, but in rekening bank it always means bank account.

Why is it tagihan itu (that bill) and not itu tagihan?

As a determiner (this/that = definiteness), itu usually follows the noun: tagihan itu. Itu before the noun is typically a pronoun or topic marker (e.g., Itu tagihan saya = That is my bill). For formal written reference to something previously mentioned, you can use tagihan tersebut.

Is lewat the best word here? How do melalui, via, dengan, and pakai compare?

All are possible, with slight register differences:

Lewat: neutral, common in speech.
Melalui: more formal/written.
Via: trendy/borrowed, informal to neutral.
Dengan/pakai: “with/using,” also fine for method. So you could say: …lewat/melalui/via transfer… or …dengan/pakai transfer….

Do I need to say ke rekening bank after transfer? Isn’t that redundant?

It’s not wrong, but it can be redundant. If context is clear, lewat transfer is enough. If you want to specify the destination, add it: …lewat transfer ke rekening [nama bank]/[nomor rekening] or …lewat transfer bank.

Should it be ke or kepada: transfer ke rekening bank vs transfer kepada rekening bank?

Use ke for destinations/targets like an account: ke rekening bank. Use kepada for recipients who are people or entities: membayar kepada penjual/perusahaan. You can combine both if you want both recipient and destination: membayar kepada perusahaan X ke rekening bank mereka.

Is ke rekening correct, or should it be di rekening?

Use ke (to) for a transfer destination: transfer ke rekening. Di (at/in) marks location, not a target, so di rekening would be odd in this context.

Can I make a passive version? How would it sound?

Yes:

Passive with agent omitted: Tagihan itu dibayar lewat transfer ke rekening bank.
Passive Type 2 (very natural): Tagihan itu saya bayar lewat transfer ke rekening bank.
With an explicit agent (less common in speech): Tagihan itu dibayar oleh saya…

Could I say this more casually?

Yes. Examples:

Aku bayar tagihan itu lewat transfer.
Gue udah bayar tagihan itu via transfer.
Aku transfer buat bayar tagihan itu.

Can transfer be a verb too?

Yes. You can say mentransfer (standard) or just transfer (informal):

Saya mentransfer uang ke rekening bank itu untuk membayar tagihan.
Saya sudah transfer ke rekening itu.

Is rekening bank the same as akun bank?

Use rekening (bank) for a bank account. Akun is mainly for online accounts/profiles. Akun bank is not the usual collocation; say rekening bank.

Can I drop Saya?

If context already makes the subject clear, you can omit it, especially with aspect markers: Sudah bayar tagihan itu lewat transfer. In careful writing, keeping saya is clearer, but omission in conversation is common.

How do I point to a specific one among many bills?

Use yang for selection: Saya membayar tagihan yang itu lewat transfer… (that specific one). For “this one,” use yang ini; for formal reference to a previously mentioned item, tagihan tersebut works well.