Ukoliko PIN ne radi, pozovite banku.

Ukoliko means if in this sentence. Yes, it is very close to ako.

The difference is mostly in style:

• ako = the most common everyday word for if
• ukoliko = a bit more formal, administrative, or written

So:

• Ako PIN ne radi, pozovite banku.
• Ukoliko PIN ne radi, pozovite banku.

Both are correct, but ukoliko sounds especially natural in instructions, notices, customer-service messages, and official writing.

Yes, raditi can mean to work in the sense of doing a job, but it also very often means to function / to operate.

So PIN ne radi literally means:

• the PIN is not working
• the PIN does not function

This is very natural Serbian.

Some examples:

• Telefon ne radi. = The phone isn’t working.
• Internet ne radi. = The internet isn’t working.
• Kartica ne radi. = The card isn’t working.

So in this sentence, radi is not about employment. It means functions.

Radi is the 3rd person singular present tense of raditi.

Here is the present tense:

• ja radim
• ti radiš
• on/ona/ono radi
• mi radimo
• vi radite
• oni/one/ona rade

Since PIN is treated as a singular thing, Serbian uses radi:

• PIN radi. = The PIN works.
• PIN ne radi. = The PIN does not work.

In Serbian, ne is usually written separately from the verb.

So:

• radi = works
• ne radi = does not work / is not working

This is the normal rule:

• ne znam = I don’t know
• ne mogu = I can’t
• ne radi = it doesn’t work

So PIN ne radi is exactly what you should expect.

Pozovite is the imperative form of pozvati, meaning call.

In this sentence, it means:

• call the bank

The ending -te shows that it is either:

1. plural imperative — speaking to more than one person, or
2. polite/formal imperative — speaking respectfully to one person

In customer instructions like this, it is usually the polite singular/plural form, similar to English instruction language:

• Please call the bank
• Call the bank

So pozovite banku is a standard polite instruction.

Because banku is the accusative singular form of banka.

Banka is a feminine noun, and here it is the direct object of pozovite:

• pozovite koga/šta? = call whom/what?
• banku

So:

• nominative: banka
• accusative: banku

This is a very common pattern for feminine nouns ending in -a:

• knjiga → knjigu
• škola → školu
• banka → banku

Because Serbian has no articles like a or the.

English says:

• the PIN
• the bank

Serbian simply says:

• PIN
• banku

Whether something means a or the is understood from context.

So pozovite banku can naturally mean call the bank without any separate word for the.

The comma separates the conditional clause from the main clause.

Structure:

• Ukoliko PIN ne radi = If the PIN does not work
• pozovite banku = call the bank

When the if-clause comes first, Serbian normally uses a comma before the main clause:

• Ako imaš vremena, dođi.
• Ukoliko PIN ne radi, pozovite banku.

This is similar to English, where a comma is also common after an opening if clause.

Yes, absolutely.

Ne funkcioniše also means doesn’t function / doesn’t work.

Compare:

• PIN ne radi = more everyday and very natural
• PIN ne funkcioniše = also correct, a bit more explicit or technical

Both are good Serbian. In short practical messages, ne radi is especially common.

In this sentence, PIN behaves like an indeclinable noun or abbreviation: it stays PIN.

You will often see PIN written in capital letters because it is an abbreviation. In everyday speech, people may pronounce it like pin.

In this sentence, no case ending is needed on PIN because it is the subject:

• PIN ne radi.

So for a learner, the important thing is simply:

• PIN = subject
• radi = singular verb agreeing with it

Yes, Serbian word order is fairly flexible, although the original sentence is the most natural for a formal instruction.

Standard version:

• Ukoliko PIN ne radi, pozovite banku.

You could also say:

• Pozovite banku ukoliko PIN ne radi.

Both are correct. The first version sounds more like a written instruction because it presents the condition first:

• If X happens, do Y.

That is why it is a very natural choice here.