Kunden reklamerer over funktionsfejlen.

In Danish, the definite article is usually added to the end of the noun.

• kunde = customer
• kunden = the customer

So unlike English, Danish often does not use a separate word like the before the noun.

For a simple definite noun, Danish normally uses the ending on the noun itself:

• funktionsfejl = functional error / malfunction
• funktionsfejlen = the functional error / the malfunction

Using den is usually for cases where there is also an adjective or some special emphasis:

• den alvorlige funktionsfejl = the serious functional error

So in this sentence, funktionsfejlen is the normal form.

It is a compound noun, which is very common in Danish.

It is made from:

• funktion = function
• fejl = error / fault

Together, funktionsfejl means something like functional fault, malfunction, or function error, depending on context.

In Danish, compound nouns are often written as one word.

Not in this sentence.

The verb at reklamere can be confusing for English speakers because it looks related to English advertise or reclaim, but here it means to make a complaint or to complain, especially in a consumer or product context.

So:

• Kunden reklamerer over funktionsfejlen. = The customer complains about the malfunction.

This is often used when a customer reports a fault in a product or service.

Because reklamere over is the pattern used here for complain about.

So:

• reklamere over noget = to complain about something

English speakers often want to translate about directly, but Danish frequently uses a different preposition than English. In this sentence, over is the natural choice.

Yes. Reklamerer is the present tense form of at reklamere.

• at reklamere = to complain
• reklamerer = complains / is complaining

So the sentence can mean:

• The customer complains about the malfunction
• or, depending on context, The customer is complaining about the malfunction

The sentence follows normal Danish main-clause word order:

• Kunden = subject
• reklamerer = verb
• over funktionsfejlen = prepositional phrase

So the pattern is:

Subject + verb + rest

That gives:

Kunden reklamerer over funktionsfejlen.

Also remember that in Danish main clauses, the finite verb normally comes in second position.

Yes, that would also be correct and natural.

• klager over = complains about
• reklamerer over = makes a complaint about, often with a more customer-service or product-fault feeling

So reklamere can sound a bit more connected to a formal complaint about a defect, purchase, or service issue, while klage is a broader verb for complaining.

Because Danish usually puts definiteness at the end of the noun instead of using a separate article.

So:

• kunden already means the customer
• funktionsfejlen already means the functional error / the malfunction

That is why you do not need a separate word for the.

It would be:

En kunde reklamerer over en funktionsfejl.

That means:

A customer complains about a functional error / a malfunction.

Compare:

• kunde = customer
• en kunde = a customer
• kunden = the customer

and

• funktionsfejl = functional error / malfunction
• en funktionsfejl = a functional error / a malfunction
• funktionsfejlen = the functional error / the malfunction

Both are common gender nouns, which is why they take en in the indefinite singular and -en in the definite singular.

• en kunde → kunden
• en funktionsfejl → funktionsfejlen

For compound nouns like funktionsfejl, the gender usually comes from the final part of the compound, here fejl.