Приложи карту к валидатору ещё раз.

Приложи is the imperative form, so it means put/tap/hold it against...!

• приложить = the dictionary form, to place against / to apply
• приложи = apply it / tap it (said to one person, informally)

So the sentence is giving an instruction, not naming the action.

This form is used when speaking to:

• one person
• in an informal way

The polite/plural version would be:

• Приложите карту к валидатору ещё раз.

Карту is the accusative singular form of карта.

That is because it is the direct object of the verb приложи: it is the thing being placed against the validator.

• nominative: карта = card
• accusative: карту = card, as the object of the action

This is very common in Russian: feminine nouns ending in -а usually change to -у in the accusative singular.

Because the preposition к requires the dative case.

• валидатор = nominative
• к валидатору = to / toward the validator

In this sentence, к means something like to / against / up to.
So приложи карту к валидатору literally means something like:

• put the card to the validator
• more naturally: hold/tap the card against the validator

Here приложить means to put something against a surface/device, not just to put in a general sense.

In transport or payment contexts, it often means:

• tap
• hold up
• place against the reader

So in this sentence it is the normal verb for using a contactless card on a machine.

It is not about applying in the English sense of applying for a job, even though some dictionaries may list apply as one meaning.

Приложить is perfective, and that fits this situation because the speaker wants one complete action:

• tap the card once more
• do it again

Russian often uses the perfective imperative when the focus is on a single completed result.

So:

• Приложи карту... = Tap the card... / Do that action now, successfully
• an imperfective version would suggest a more process-like, repeated, or habitual idea

In this context, perfective is the most natural choice.

Ещё раз means once again / one more time / again.

In this sentence, it tells the person to repeat the action:

• Приложи карту к валидатору ещё раз.
• Tap the card on the validator one more time.

A useful point:

• ещё on its own often means still / yet / more
• раз means time in expressions like one time
• together, ещё раз = again / one more time

Yes, often you can.

For example:

• Приложи карту к валидатору снова.

This would also mean Tap the card again.

But there is a slight nuance:

• ещё раз strongly emphasizes one more attempt
• снова simply means again

In a real-life instruction from a driver, inspector, or machine-related situation, ещё раз sounds especially natural because it suggests: try it one more time.

Yes, in transport contexts it is common. Валидатор is the machine that reads or validates a ticket, travel card, or bank card.

Depending on the situation, English might translate it as:

• validator
• card reader
• ticket validator
• payment terminal (sometimes, depending on the exact device)

So although validator is not always the most natural everyday English word, валидатор is normal Russian for this kind of device.

Yes. Russian word order is fairly flexible, and the basic meaning would stay the same.

For example, you could also hear:

• Ещё раз приложи карту к валидатору.
• К валидатору приложи карту ещё раз.

But the original order is very natural:

• Приложи карту к валидатору ещё раз.

Why this order works well:

• verb first = direct instruction
• then the object карту
• then where to put it к валидатору
• then ещё раз = repeat the action

So the sentence sounds straightforward and practical.

Use the plural/polite imperative:

• Приложите карту к валидатору ещё раз.

This can mean either:

• speaking politely to one person
• speaking to multiple people

So the contrast is:

• Приложи = informal singular
• Приложите = polite singular or plural

A careful pronunciation with stress marks is:

• Приложи́ ка́рту к валидáтору ещё́ раз.

Roughly:

• pri-la-ZHEE KAR-tu k va-li-DA-ta-ru ye-SHCHO raz

A few helpful notes:

• ещё is pronounced with shch-like sound: ye-SHCHO
• к is very short, almost attached to the next word
• приложи́ has the stress at the end

In normal speech, the whole sentence is usually said quite smoothly, especially in a transport setting.