Learn Hardcore Malay: Resit ini bukti saya sudah bayar bil. - This receipt is proof that I have already paid the bill.

ialah before a noun complement: Resit ini ialah bukti…
adalah is widely used, especially before adjectives/prepositional phrases; many people also use it before nouns in practice.
merupakan (“constitutes”) is a safe, formal choice: Resit ini merupakan bukti…

Do I need the word for “that” (bahawa) after bukti? Why is it omitted?

It’s optional. Spoken Malay often omits bahawa:

Both are correct. Adding bahawa makes the clause boundary clearer, especially in writing.

Can I say bukti yang saya sudah bayar bil?

Not like that. yang introduces a relative clause that modifies a noun. You’d need a verb like “show”:

bukti yang saya sudah bayar bil is ungrammatical.

What’s the difference between sudah, telah, and dah?

All mark completed action:

sudah: neutral, common in speech and writing.
telah: more formal/literary.
dah: colloquial contraction of sudah. Example: saya sudah/dah/telah bayar = I have already paid.

How is pernah different from sudah?

pernah means “has/have ever (at some time before).” It doesn’t assert completion of the specific current action.

saya sudah bayar = I have already paid (this time).
saya pernah bayar = I have paid before (at some point in the past; not necessarily this bill/occasion).

Why use bayar instead of membayar? Are both correct?

Yes, both are correct.

bayar (base verb) is common and natural in speech: saya sudah bayar bil
membayar (meN- form) is more formal: saya telah membayar bil Meaning is the same; it’s a register choice.

Can I make it passive, like “the bill has been paid”?

Yes:

Resit ini bukti bil itu sudah dibayar. You can add the agent if needed: … sudah dibayar oleh saya, but Malay often omits the agent when it’s obvious.

Should it be bil itu or bil saya to be specific?

Malay has no articles, so specificity comes from context or demonstratives/possessives:

Do I need a classifier with resit (like “a piece of”)? What’s natural?

You can use one when counting:

sekeping resit / sehelai resit = one receipt (both are used; sekeping is common for flat items) But you don’t need a classifier with a specific noun phrase:
resit ini = this receipt (natural)

Where exactly does sudah go? Can I say bayar sudah?

Place aspect markers like sudah/telah/dah before the verb:

Natural: saya sudah bayar bil
bayar sudah is not standard; you might hear it for special emphasis in some dialects, but avoid it in normal usage.

Is the sentence formal or casual? How would I make it more formal?

The given sentence is neutral–informal. More formal options:

What’s the difference between resit, bil, and invois?

resit = receipt (proof of payment already made)
bil = bill (an amount to be paid; a tab)
invois = invoice (formal billing document) Your sentence uses both ends: resit (proof) and bil (what was paid).

How do I say “proof of payment” as a set phrase?

Use bukti pembayaran. Example: Ini bukti pembayaran untuk bil itu.

Can I drop saya in the clause saya sudah bayar bil?

In casual speech, subjects can be dropped if clear from context:

Resit ini bukti dah bayar bil. However, including saya is clearer and preferred in neutral/formal contexts.

How do I pronounce the key words?

Approximate English-friendly pronunciation:

How do I make “bills” plural?

Malay doesn’t require plural marking. Use context or quantifiers: