Disculpe la molestia, pero no encuentro el justificante del pago.

Disculpe is the formal way to say excuse me / sorry to one person in Spanish.

• disculpa = informal, used with tú
• disculpe = formal, used with usted

So this sentence is addressing someone politely, such as a clerk, receptionist, or customer-service person.

In Spain, related forms are:

• disculpa = informal singular
• disculpe = formal singular
• disculpad = informal plural (vosotros)
• disculpen = formal plural (ustedes)

Here la molestia means the inconvenience, the bother, or the trouble you may be causing someone.

So Disculpe la molestia is a polite expression similar to:

• Sorry for the inconvenience
• Sorry to bother you
• Excuse the trouble

It does not usually mean a physical pain or medical problem here. It is an everyday politeness phrase.

Yes, las molestias is also possible, and in fact very common in polite Spanish.

The difference is small:

• la molestia = the inconvenience/trouble as a single idea
• las molestias = the inconveniences/trouble caused, often as a set phrase

In this sentence, Disculpe la molestia sounds natural and polite.
You may also hear:

• Perdone las molestias
• Siento las molestias

All are acceptable, with slightly different phrasing but very similar meaning.

No encuentro is the most natural and direct way to say I can’t find or I’m not finding something in this situation.

Spanish often uses the simple present where English might use:

• I can’t find
• I’m unable to find
• I’m not finding

So:

• No encuentro el justificante = I can’t find the receipt/proof

You could say no puedo encontrar, but it sounds a bit heavier or more emphatic.
In everyday speech, no encuentro is usually enough.

It comes from the verb encontrar = to find.

This verb has a stem change in the present tense:

• yo encuentro
• tú encuentras
• él/ella/usted encuentra
• nosotros encontramos
• vosotros encontráis
• ellos/ellas/ustedes encuentran

The change is o → ue in most forms, but not in nosotros and vosotros.

So encuentro is the correct yo form.

Justificante is a very useful word in Spain. It usually means proof, supporting document, or official evidence that something happened.

So el justificante del pago means something like:

• the proof of payment
• the payment receipt
• the payment confirmation
• the document showing the payment was made

This could be:

• a bank transfer confirmation
• a receipt
• a printed payment slip
• a PDF or email confirming payment

In Spain, justificante often sounds a bit more official or administrative than just receipt.

Del is the contraction of de + el.

So:

• de el pago → del pago

This contraction is required in normal Spanish.

Here it means of the payment:

• el justificante del pago = the proof/receipt of the payment

This is one of the most common contractions in Spanish:

• de + el = del
• a + el = al

Yes, both are possible, but the nuance is slightly different.

• justificante de pago = proof of payment as a general type of document
• justificante del pago = the proof of the payment, often referring to a specific payment already known in context

In your sentence, del pago sounds like there is a particular payment being discussed, which is very natural.

So:

• No encuentro el justificante de pago = I can’t find the payment receipt/proof
• No encuentro el justificante del pago = I can’t find the proof of that payment

Both can work.

Because the speaker usually means a specific document that both sides understand.

• el justificante = the receipt/proof, the one connected to this payment
• un justificante = a receipt/proof, any one

In practical situations, there is normally one expected document, so the definite article is the natural choice.

Yes, it is clearly formal and polite.

The main sign is disculpe, which uses usted. The whole sentence sounds suitable for:

• talking to office staff
• speaking to customer service
• contacting a company
• asking a receptionist or administrator for help

An informal version would be:

• Disculpa la molestia, pero no encuentro el justificante del pago.

Sometimes, but they are not always exact matches.

In Spain:

• justificante is very common for official proof, especially in banking, administration, or payments
• recibo often means a receipt or a bill/charge notice, depending on context
• comprobante is understood, but it is generally more common in many Latin American varieties than in Spain

So for Spain, justificante is a very natural choice here.

In Spanish, the basic negative structure is:

• no + verb

So:

• encuentro = I find
• no encuentro = I do not find / I can’t find

That is the normal position of no in simple sentences. It goes directly before the conjugated verb.

So this sentence follows the standard pattern perfectly:

• no encuentro el justificante del pago