Dowód zakupu jest w potwierdzeniu zamówienia.

Because zakupu is in the genitive case. In Polish, when one noun explains another noun like proof of purchase, the second noun is often put in the genitive.

• dowód = proof
• zakup = purchase
• dowód zakupu = proof of purchase

This is a very common pattern in Polish:

• numer telefonu = phone number
• potwierdzenie zamówienia = order confirmation
• data urodzenia = date of birth

So zakupu means of purchase, not just purchase.

Because the preposition w meaning in usually requires the locative case.

The base form is:

• potwierdzenie = confirmation

After w, it becomes:

• w potwierdzeniu = in the confirmation

So:

• jest w potwierdzeniu = is in the confirmation

This is a normal case change after prepositions in Polish.

Because potwierdzenie zamówienia means confirmation of the order or order confirmation.

Here, zamówienia is in the genitive case, because it depends on potwierdzenie in the same way that zakupu depends on dowód.

Breakdown:

• potwierdzenie = confirmation
• zamówienie = order
• potwierdzenie zamówienia = confirmation of the order

So the sentence contains two noun + genitive combinations:

• dowód zakupu
• potwierdzenie zamówienia

Jest means is. It is the 3rd person singular form of być = to be.

So:

• Dowód zakupu jest w potwierdzeniu zamówienia. = The proof of purchase is in the order confirmation.

In the present tense, Polish often omits to be in some kinds of sentences, especially when linking two nouns or adjectives:

• On jest miły can become On miły only in very limited, non-standard or poetic contexts, so usually jest stays.

In this sentence, jest sounds fully natural and should normally be kept. Omitting it would sound wrong in standard Polish:

• Dowód zakupu w potwierdzeniu zamówienia is not a normal full sentence here.

Not exactly. Dowód zakupu is broader than English receipt.

It means proof of purchase, so it could be:

• a receipt
• an invoice
• an order confirmation
• some other document showing that you bought something

A very common Polish word for a shop receipt is:

• paragon

So:

• paragon = receipt from a shop or cash register
• dowód zakupu = proof of purchase in a more general sense

That is why this sentence can say the proof of purchase is in the order confirmation.

In this sentence, w means in, so the idea is that the proof of purchase is contained in the order confirmation.

• w potwierdzeniu = in the confirmation

You may sometimes hear na with documents or pages when something is physically on them:

• na fakturze = on the invoice
• na stronie = on the page

But here w potwierdzeniu zamówienia is natural because the information is understood as being included inside the content of that confirmation.

So for this sentence, w is the best choice.

The basic word order here is natural and neutral:

• Dowód zakupu jest w potwierdzeniu zamówienia.

Polish word order is more flexible than English, because case endings show grammatical relationships. So you could change the order for emphasis, for example:

• W potwierdzeniu zamówienia jest dowód zakupu.

This puts more focus on where the proof of purchase is.

But the original version is the most neutral and straightforward.

They are related, but not the same.

• zakup = purchase, the act/result of buying
• zamówienie = order, especially something you place online or request from a seller

So:

• dowód zakupu = proof that the purchase happened
• potwierdzenie zamówienia = confirmation of the order

In many online shopping situations, the order confirmation can serve as proof of purchase.

It sounds neutral to slightly formal, which is very common for customer service, e-commerce, and official information.

Words like:

• dowód zakupu
• potwierdzenie zamówienia

are typical in:

• online shops
• return policies
• warranty information
• help pages

In everyday casual speech, someone might choose simpler wording depending on context, but this sentence is completely natural and standard.

Polish stress usually falls on the second-to-last syllable of each word.

Roughly:

• DO-wód
• za-KU-pu
• jest
• w po-twier-DZE-niu
• za-mó-WIE-nia

In a full sentence, the main stress would usually fall naturally on the important content words, especially near the end:

• Dowód zakupu jest w potwierdzeniu zamówienia.

If someone wants to emphasize the location, they might stress potwierdzeniu zamówienia more strongly.