Diesen Kassenbon solltest du aufheben, falls du das Waschpulver wegen des Sonderangebots umtauschen willst.

Because Kassenbon is the direct object of aufheben, so it has to be in the accusative case.

• dieser Kassenbon = nominative masculine
• diesen Kassenbon = accusative masculine

The verb phrase is einen Kassenbon aufheben = to keep/save a receipt, so the sentence needs the accusative form diesen.

Both are correct.

German often moves something to the front of the sentence for emphasis or topic. By starting with Diesen Kassenbon, the speaker highlights this receipt in particular.

So:

• Du solltest diesen Kassenbon aufheben. = neutral word order
• Diesen Kassenbon solltest du aufheben. = stronger focus on this receipt

Because German main clauses require the finite verb in second position, once Diesen Kassenbon is placed first, solltest must come next, and du follows after it.

This happens because the sentence starts with Diesen Kassenbon. In a German main clause, the finite verb must be the second element.

So the structure is:

1. Diesen Kassenbon
2. solltest
3. du
4. aufheben

This is called inversion from an English-speaking learner's point of view, but in German it is just normal verb-second word order.

Here solltest means should in the sense of advice or recommendation.

So Diesen Kassenbon solltest du aufheben means something like:

• You should keep this receipt
• It would be a good idea to keep this receipt

It is softer than a strong command.

Compare:

• Du musst den Kassenbon aufheben. = You must keep the receipt.
• Du solltest den Kassenbon aufheben. = You should keep the receipt.

Because aufheben is paired with the modal verb solltest.

With modal verbs in German, the modal is the conjugated verb and the main verb stays in the infinitive at the end:

• du solltest aufheben
• du willst umtauschen
• ich kann kommen

So in this clause:

• solltest = finite modal verb
• aufheben = infinitive at the end

Yes, aufheben is a separable verb.

Without a modal verb, it would split in a main clause:

• Du hebst den Kassenbon auf.

But with a modal verb, the separable verb stays together in the infinitive:

• Du solltest den Kassenbon aufheben.

So it is still the same verb, just not split because of the modal construction.

Falls means in case or if and introduces a conditional subordinate clause.

In this sentence, it means:

• keep the receipt in case you want to exchange the washing powder

It is similar to wenn, but falls often sounds a bit more specific or precautionary, as in if that situation happens.

Compare:

• falls du ... willst = in case you want to ...
• wenn du ... willst = if you want to ...

In many contexts, both are possible, but falls fits especially well when giving advice about a possible future situation.

Because falls introduces a subordinate clause, and German requires a comma before subordinate clauses.

So:

• Diesen Kassenbon solltest du aufheben, falls ...

This is standard German punctuation, not optional.

Because the clause starting with falls is a subordinate clause, and in German subordinate clauses the conjugated verb normally goes to the end.

So:

• falls du das Waschpulver wegen des Sonderangebots umtauschen willst

The order is:

• falls = subordinating conjunction
• du = subject
• other elements in the middle
• willst = finite verb at the end

This is one of the most important German word-order patterns to get used to.

Traditionally, wegen takes the genitive, so standard written German prefers:

• wegen des Sonderangebots

Here:

• das Sonderangebot = nominative/accusative
• des Sonderangebots = genitive singular

The ending -s on Sonderangebots is the normal genitive ending for many neuter nouns.

You may hear wegen dem Sonderangebot in colloquial speech, because many speakers use the dative after wegen, but wegen des Sonderangebots is the standard form learners are usually taught first.

Umtauschen means to exchange something, usually by returning it and getting another item instead.

So here it suggests that the person may want to take the washing powder back because of the special-offer situation and exchange it.

Related verbs:

• umtauschen = exchange
• zurückgeben = return
• tauschen = swap/exchange more generally

Umtauschen is a very common verb in shopping contexts, especially when talking about receipts, stores, and products.

German often uses the definite article where English might or might not use one.

Here das Waschpulver refers to a specific product already understood in the situation: the washing powder in question.

This does not necessarily mean it was mentioned earlier in the sentence. German often uses the article simply because the item is concrete and identifiable from context.

So das Waschpulver sounds natural, just like:

• den Kassenbon
• die Jacke
• das Produkt

in shopping-related situations.