Το τιμολόγιο γράφει ότι μετά την τελευταία πληρωμή το υπόλοιπο είναι μικρό.

Το τιμολόγιο means the invoice. It is the subject of the verb γράφει, so it is in the nominative case.

• το = the (neuter singular)
• τιμολόγιο = invoice

The noun τιμολόγιο is neuter, which is why it takes το.

Greek often uses γράφει literally as writes, but with things like documents, signs, labels, messages, and screens, it commonly means says or states in English.

So:

• Το τιμολόγιο γράφει ότι... = The invoice says/states that...

This is very natural Greek. English does something similar too: The sign says...

Ότι introduces a clause, just like that in English.

So:

• γράφει ότι... = says that...

It connects the main clause to the information being reported.

A useful detail:

• ότι = that
• ό,τι = whatever / anything that

Those are different words, even though they look very similar.

Because μετά meaning after is followed by the accusative case in Modern Greek.

So:

• μετά = after
• την πληρωμή = the payment (accusative singular)

Since πληρωμή is feminine singular, the article and adjective must match it:

• την = feminine singular accusative
• τελευταία = feminine singular accusative
• πληρωμή = feminine singular accusative

That is why you get μετά την τελευταία πληρωμή = after the last payment.

Greek uses the definite article more often than English. Here, την τελευταία πληρωμή refers to a specific payment, namely the last payment, so the article is expected.

Also, with adjectives like τελευταίος / τελευταία / τελευταίο meaning last, Greek normally uses the article when talking about a specific known thing:

• η τελευταία φορά = the last time
• το τελευταίο μάθημα = the last lesson
• την τελευταία πληρωμή = the last payment

Το υπόλοιπο means the remainder, the balance, or the amount left.

In financial contexts, it usually means the remaining balance or the outstanding balance.

So in this sentence:

• το υπόλοιπο = the balance remaining after payment

It is a neuter noun, which is why it uses το.

Because adjectives in Greek must agree with the noun they describe.

Here, the noun is:

• το υπόλοιπο — neuter singular

So the adjective must also be neuter singular:

• μικρό = small / low

Compare:

• μικρός = masculine singular
• μικρή = feminine singular
• μικρό = neuter singular

Since υπόλοιπο is neuter, μικρό is the correct form.

Literally, μικρό means small, but in this context English would often say low.

So:

• το υπόλοιπο είναι μικρό can mean
  • the balance is small
  • the balance is low

Both ideas are correct. Greek naturally uses small here where English may prefer low in financial language.

Greek word order is fairly flexible. The sentence as written is natural and clear:

• Το τιμολόγιο γράφει ότι μετά την τελευταία πληρωμή το υπόλοιπο είναι μικρό.

Placing μετά την τελευταία πληρωμή before το υπόλοιπο είναι μικρό helps set the time frame first: after the last payment...

You could also say:

• Το τιμολόγιο γράφει ότι το υπόλοιπο είναι μικρό μετά την τελευταία πληρωμή.

That is understandable, but the original version sounds a bit smoother and more natural for written or formal information.

Yes, in many cases πως can also introduce a clause meaning that:

• Το τιμολόγιο γράφει πως...

That is possible and natural. However, ότι often feels a bit more neutral or formal in writing, so it fits well here.

A useful distinction:

• πως = that
• πώς = how

The accent matters with πώς, but in everyday writing people are sometimes less strict with this than in formal grammar explanations.

Yes, sometimes. Depending on context, these are all possible translations:

• The invoice says that...
• The invoice states that...
• The invoice reads...

In normal English, says or states is usually the most natural translation here. Reads is possible, but it is less common in everyday speech.