Al facturar el bulto, conservé el comprobante de facturación.

Al + infinitive is a very common Spanish structure meaning when, upon, or while doing something.

So:

• al facturar el bulto = when checking in the package/item
• more literally: upon checking in the package/item

It usually introduces an action that happens at the same time as, or immediately before, the main action.

Examples:

• Al llegar, llamé a casa. = When I arrived, I called home.
• Al abrir la puerta, vi al perro. = When I opened the door, I saw the dog.

In your sentence, it means that the speaker kept the receipt at the moment they checked in the item.

Because after al, Spanish uses the infinitive, not a conjugated verb.

So you say:

• al facturar
• al salir
• al entrar

Not:

• al facturé
• al salí
• al entré

This is just how the structure works grammatically:

• al
  • infinitive

If you wanted a fully conjugated clause instead, you would need something like:

• Cuando facturé el bulto, conservé el comprobante.

That means almost the same thing: When I checked in the item, I kept the receipt.

That is a very good question, because facturar has more than one meaning.

Depending on context, facturar can mean:

1. to invoice / to bill
2. to check in luggage
3. sometimes to consign/send goods

In this sentence, it most likely means to check in or to process an item/baggage/package for transport, not to issue an invoice.

That is why context matters a lot. In travel and transport contexts, especially with luggage or shipped items, facturar often refers to formally handing over the item so it can be transported.

Bulto is a somewhat broad word. It can mean:

• a package
• a bundle
• a parcel
• a piece/item, especially in transport contexts
• sometimes a piece of luggage

Here it refers to the physical item being checked in or sent.

It is not as specific as maleta (suitcase) or paquete (package). It is more general.

In transport language, bulto often means something like:

• piece
• item
• package
• lump/bundle

So the exact English translation depends on the situation.

Conservé is the first-person singular preterite of conservar.

• yo conservé = I kept / I retained

The preterite is used here because the speaker is describing a completed action in the past.

So the sentence presents two past actions:

• al facturar el bulto = when checking in the item
• conservé el comprobante = I kept the receipt

This sounds like a completed past event, not a habit or ongoing action.

Compare:

• Conservé el comprobante. = I kept the receipt.
• Conservaba el comprobante. = I was keeping / used to keep the receipt.

The preterite is the natural choice here.

Conservar means to keep, to retain, or to preserve.

In this sentence, conservé el comprobante means the speaker kept hold of the receipt and did not throw it away or lose it.

You could also see guardar in similar contexts:

• Guardé el comprobante. = I kept/saved the receipt.

The difference is subtle:

• guardar often means to put away, to save, to store
• conservar often emphasizes retaining something, continuing to have it

In many contexts, both are possible, but conservar sounds a bit more formal or deliberate here.

Comprobante means proof, receipt, voucher, or document confirming something.

So comprobante de facturación means something like:

• check-in receipt
• proof of check-in
• receipt for the checked item
• confirmation document of the check-in process

The phrase de facturación specifies what kind of receipt it is: one related to facturación, the check-in/processing of the item.

So literally it is something like:

• receipt of check-in
• check-in document

Because Spanish often uses noun + de + noun where English might use a noun as an adjective.

So:

• comprobante de facturación = literally receipt of check-in = more naturally in English, check-in receipt

Other examples:

• billete de tren = train ticket
• mesa de madera = wooden table
• tarjeta de crédito = credit card

So de is just linking the two nouns in a very normal Spanish way.

Spanish uses definite articles more often than English does.

Here:

• el bulto = the item/package being checked in
• el comprobante = the relevant receipt

Even if English might sometimes say I checked in a package and kept the receipt, Spanish often uses el when the thing is understood in context.

This does not always mean the speaker expects the listener to know exactly which object in advance. It can simply refer to the relevant item in the situation.

So the articles sound natural here.

Yes, the exact English nuance can vary depending on context.

Al + infinitive often covers meanings like:

• when
• upon
• while
• sometimes after, if the sequence is immediate

So Al facturar el bulto, conservé el comprobante could be understood as:

• When I checked in the item, I kept the receipt
• Upon checking in the item, I kept the receipt
• After checking in the item, I kept the receipt

The core idea is that the action of keeping the receipt happened in direct connection with the check-in process.

It is understandable, but it sounds a bit formal and somewhat technical.

In Spain, depending on the context, people might say something more natural like:

• Al facturar el equipaje, guardé el resguardo.
• Cuando facturé el paquete, guardé el comprobante.
• Al facturar la maleta, me quedé con el resguardo.

A few notes:

• equipaje or maleta may sound more natural than bulto if it is luggage
• resguardo can sound more idiomatic in Spain than comprobante in some contexts
• guardé is often more everyday than conservé

So the original sentence is correct and understandable, but it is not the most colloquial possible version.

Usually not. If you are talking about air travel, more common words would often be:

• equipaje = luggage
• maleta = suitcase
• bolsa = bag

For example:

• Al facturar la maleta, conservé el resguardo.
• Al facturar el equipaje, guardé el comprobante.

Bulto is broader and can fit logistics, shipping, freight, or general transport language. It sounds less specific than what many people would use for ordinary passenger travel.

Yes. That is one of the most straightforward alternatives.

Compare:

• Al facturar el bulto, conservé el comprobante de facturación.
• Cuando facturé el bulto, conservé el comprobante de facturación.

Both mean roughly the same thing.

Difference in feel:

• al + infinitive is a bit more compact and slightly more formal/written
• cuando + conjugated verb is often more direct and easier for learners to understand

So if you are speaking and want something simpler, cuando facturé... is an excellent option.