A la caixa, he pagat amb una moneda i no m'han tornat tot el canvi.

A la caixa means at the checkout / at the cash register / at the till.

• caixa literally means box, but in shop language it commonly means the cash register or the checkout area.
• The preposition a here means at.

So A la caixa sets the scene: at the checkout.

The comma shows it is being used as a fronted location phrase:

• A la caixa, he pagat... = At the checkout, I paid...

You could also say the sentence without that opening phrase if the context is already clear.

He pagat is the present perfect in Catalan:

• he = I have
• pagat = past participle of pagar (paid)

So literally it is I have paid.

Catalan uses this structure with forms of haver + past participle:

• he pagat = I have paid
• has pagat = you have paid
• ha pagat = he/she has paid

A learner may expect vaig pagar because that is also a common past tense in Catalan, especially in general narration. Both can refer to past events, but he pagat often fits well when the action is connected to the present situation, especially in many everyday contexts.

Amb means with.

So:

• he pagat amb una moneda = I paid with a coin

It introduces the means or instrument used to pay.

Examples:

• Paga amb targeta. = Pay by card.
• Ho he escrit amb un llapis. = I wrote it with a pencil.

So here amb una moneda tells you what was used for the payment.

It can mean both, depending on context.

In this sentence, una moneda clearly means a coin.

But moneda can also mean currency in a broader sense:

• la moneda europea = the European currency
• la moneda local = the local currency

If you want to contrast:

• moneda = coin / currency
• bitllet = banknote / bill

So here una moneda definitely means a coin, not currency in general.

The m' is the weak pronoun meaning to me.

So:

• no m'han tornat... = they haven’t given me back...

More literally:

• m' = to me
• han tornat = they have returned / given back

This pronoun is needed because the sentence means that someone did not return something to me.

Compare:

• No han tornat el llibre. = They didn’t return the book.
• No m'han tornat el llibre. = They didn’t return the book to me.

The apostrophe appears because em becomes m' before a vowel:

• em han tornat → m'han tornat

Catalan often omits subject pronouns when they are understood from the verb ending.

So han tornat literally means they have returned, but the subject they is not stated because it is obvious from han.

In this sentence, it refers to the people at the checkout, cashier, or shop staff in a general sense:

• no m'han tornat... = they didn’t give me back...

This is very natural in Catalan.

Yes. Tornar often means to return, but in money contexts it is very commonly used for to give back.

So:

• tornar el canvi = to give back the change
• m'han tornat... = they gave me back...

This is standard everyday Catalan.

A very common expression is:

• Tornar el canvi = to give someone their change

So even though the basic idea is return, the natural English translation here is give back.

Tot el canvi means all the change.

Breaking it down:

• tot = all / the whole of
• el canvi = the change

So the idea is:

• they didn’t give me all the change I was supposed to receive

In English we often say:

• They didn’t give me all my change
• They didn’t give me the full change

Catalan uses tot el canvi very naturally for that idea.

Because canvi here is a specific, identifiable thing: the change from this payment.

That is why the definite article el is used:

• tot el canvi = all the change

Without the article, tot canvi would not sound natural here.

This is similar to English, where we also normally say all the change, not all change, in this situation.

No. Canvi can mean change in more than one sense.

1. Money change

   • No m'han tornat el canvi. = They didn’t give me the change back.

2. Change / alteration / switch

   • un canvi de plans = a change of plans
   • canvi climàtic = climate change

In this sentence, because of pagat and moneda, it clearly means change in money.

In Catalan, no usually goes directly before the verb, or before any weak pronouns attached to the verb phrase.

So:

• m'han tornat = they have given me back
• no m'han tornat = they have not given me back

This is the normal position for negation.

Examples:

• No he pagat. = I haven’t paid.
• No m'ho han dit. = They haven’t told me that.

So the order here is perfectly regular:

• no
  • m'
    • han tornat

Yes, the word order is natural.

The sentence starts with A la caixa to set the context first:

• A la caixa, he pagat amb una moneda...

That sounds like:

• At the checkout, I paid with a coin...

But Catalan allows other natural orders too, for example:

• He pagat amb una moneda a la caixa i no m'han tornat tot el canvi.
• No m'han tornat tot el canvi a la caixa.

The original version sounds slightly more narrative or scene-setting because it opens with the location.

The comma marks A la caixa as an introductory phrase.

It is similar to English punctuation in:

• At the checkout, I paid with a coin...

The sentence would still be understandable without the comma in informal writing, but the comma helps separate the setting from the main statement.

It is grammatically fine, but in real life it may depend on context.

If someone says:

• He pagat amb una moneda

it suggests they used a single coin, perhaps a coin of enough value for the purchase, or that the specific fact that it was a coin matters.

In everyday speech, people might also say:

• He pagat amb monedes. = I paid with coins.
• He pagat amb un bitllet. = I paid with a banknote.
• He pagat en efectiu. = I paid in cash.

So the sentence is natural, especially if the point is that one coin was used.

A more literal breakdown would be:

• A la caixa = At the checkout
• he pagat = I have paid
• amb una moneda = with a coin
• i = and
• no m'han tornat = they haven’t returned to me / given me back
• tot el canvi = all the change

So a very literal version is:

At the checkout, I have paid with a coin and they haven’t given me back all the change.

That is more literal than natural English, but it helps show how the Catalan sentence is built.