Nawet jeśli znasz odbiorcę przelewu, uwierzytelnij transakcję.

Nawet jeśli means even if and introduces a condition that does not change the main instruction.

• jeśli = if
• nawet jeśli = even if

So the structure is:

• Nawet jeśli ... , ...
• Even if ... , ...

You could also see nawet jeżeli. That means the same thing; jeśli is just a bit more common in everyday Polish.

Znasz is the 2nd person singular present tense form of znać.

• znać = to know, to be familiar with
• znasz = you know

It matches the person being addressed in uwierzytelnij:

• znasz = you know
• uwierzytelnij = authenticate!

So the whole sentence is addressing one user directly.

Because Polish splits English to know into different verbs.

• znać is used for knowing a person / place / thing, being familiar with it
• wiedzieć is used for knowing a fact

So:

• znać odbiorcę = to know the recipient
• wiedzieć, kim jest odbiorca = to know who the recipient is

Since this sentence means you are familiar with the recipient, znać is the correct verb.

Because odbiorcę is the accusative singular form, and it is the direct object of znasz.

Dictionary form:

• odbiorca = recipient

In the sentence:

• znasz kogo? → odbiorcę

This noun can be confusing because it ends in -a but is masculine personal, not feminine. Its forms look like this:

• nominative: odbiorca
• accusative: odbiorcę
• genitive: odbiorcy

So znasz odbiorcę is grammatically exactly what Polish requires.

Przelewu is the genitive singular of przelew.

• przelew = bank transfer
• przelewu = of the transfer

In odbiorca przelewu, Polish uses the genitive to express the relationship that English often expresses with of:

• odbiorca przelewu = recipient of the transfer

So here:

• odbiorcę przelewu = the recipient of the transfer

Uwierzytelnij is an imperative form, meaning it gives an instruction or command:

• uwierzytelnić = to authenticate
• uwierzytelnij = authenticate!

In banking and security language, this is very common. It tells the user to complete the authentication step.

This verb is also perfective, which fits the idea of a single completed action: authenticate this transaction now.

Because transakcję is the accusative singular form of transakcja, and it is the direct object of the imperative verb.

• transakcja = transaction
• uwierzytelnij transakcję = authenticate the transaction

For many feminine nouns ending in -a, the accusative singular changes to -ę:

• transakcja → transakcję
• operacja → operację

Grammatically, it is the singular imperative, which is the form used when speaking directly to one person.

In English, apps often say things like:

• Confirm the payment
• Verify your identity

Polish interfaces do the same thing. So uwierzytelnij transakcję is not necessarily rude or unusually informal; it is a normal direct instruction to the user.

A more formally polite version would usually be phrased differently, for example with proszę:

• Proszę uwierzytelnić transakcję.

But in app and website text, the short imperative is very standard.

Because Nawet jeśli znasz odbiorcę przelewu is a subordinate clause, and in Polish such clauses are normally separated by a comma from the main clause.

So:

• Nawet jeśli znasz odbiorcę przelewu, uwierzytelnij transakcję.

If you reversed the order, the comma would still be there:

• Uwierzytelnij transakcję, nawet jeśli znasz odbiorcę przelewu.

The original order puts the condition first, which makes the warning feel slightly stronger.