El rebut domiciliat arriba avui.

Here domiciliat means something like set up as a direct debit or paid through a bank account automatically.

It is the past participle of domiciliar, but in this sentence it works like an adjective describing rebut.

So rebut domiciliat is not just any bill/receipt: it is one that is bank-debited / direct-debited.

In Catalan, adjectives often come after the noun, especially when they classify or describe it in a fairly objective way.

So:

• el rebut domiciliat = the direct-debit bill/payment notice

This is more natural in Catalan than putting the adjective first.

Rebut can mean receipt, but in financial contexts it often means bill, charge notice, or payment receipt.

Because the sentence says domiciliat, the most likely meaning here is something like:

• a bill paid by direct debit
• a direct-debit charge
• a payment notice linked to your bank account

So even though rebut can mean receipt, here it is probably better understood in a banking/billing sense.

El is the masculine singular definite article, meaning the.

It is used because the speaker is referring to a specific bill/payment notice, not just any one in general.

• el rebut = the bill / the receipt

Catalan often uses the definite article in places where English might also use the, and sometimes even where English would leave it out.

Arriba is the 3rd person singular present indicative of arribar (to arrive).

So grammatically it means:

• it arrives
• it is arriving
• sometimes even it comes

Here the subject is el rebut domiciliat, so:

• El rebut domiciliat arriba avui = The direct-debit bill arrives today

Catalan often uses the present tense for things that are scheduled, expected, or happening in the near future.

So arriba avui can sound very natural for:

• something due today
• something expected today
• something scheduled for today

Using arribarà avui is also possible, but it may sound a little more explicitly future-oriented.
The present tense here feels immediate and natural.

Because rebut is masculine singular, the adjective/participle must also be masculine singular:

• rebut domiciliat

If the noun were feminine singular, it would change:

• factura domiciliada

If it were plural:

• rebuts domiciliats
• factures domiciliades

So domiciliat matches rebut in gender and number.

Yes. Catalan word order is flexible, though the original sentence is very natural.

For example, you could also say:

• Avui arriba el rebut domiciliat.

This puts more emphasis on avui (today).

The original:

• El rebut domiciliat arriba avui.

is a neutral, straightforward word order: subject + verb + time expression.

It is originally a past participle, but here it functions adjectivally.

That is very common in Catalan. A participle can behave like an adjective and describe a noun:

• un compte tancat = a closed account
• una carta enviada = a sent letter
• el rebut domiciliat = the direct-debit bill/payment notice

So in this sentence, it is best understood as a descriptive modifier of rebut.

A simple approximate pronunciation is:

• el ruh-BUT doh-mee-see-lee-AT ah-RREE-bah ah-BOO-ee

A few helpful points:

• rebut has stress on the last syllable: re-BUT
• domiciliat has stress near the end: domicili-AT
• arriba has a trilled or tapped r
• avui sounds roughly like ah-BOO-ee

Pronunciation varies somewhat by dialect, but this will guide you well.