Når først købsdatoen er fundet, ved kunden, at reklamationsretten gælder.

Når først is a very common Danish pattern meaning something like once or when ... has been established.

• når = when
• først adds the sense of once / once it has finally been done

So Når først købsdatoen er fundet is not just a neutral when the purchase date is found, but more like:

• once the purchase date has been found
• once the purchase date is known

Here, først does not literally mean first in the usual English sequence sense. It adds emphasis that this first condition must be met before the next thing follows.

Because -en at the end makes the noun definite.

• en købsdato = a purchase date
• købsdatoen = the purchase date

Danish often attaches the definite article to the end of the noun instead of using a separate word like the.

Also, købsdato is a compound noun:

• køb = purchase
• dato = date
• købsdato = purchase date

Then the definite ending is added to the whole compound:

• købsdatoen = the purchase date

It looks a bit like both from an English learner’s point of view, but here it is best understood as a passive/resultative construction.

• finde = to find
• fundet = found
• er fundet = is found / has been found

In this sentence, købsdatoen er fundet means the purchase date has been identified or established. It focuses on the result rather than on who found it.

So Danish is not saying who did the action. It is simply saying that the purchase date is now known.

Compare:

• Kunden har fundet købsdatoen = The customer has found the purchase date
• Købsdatoen er fundet = The purchase date has been found

This is because Danish uses verb-second word order in main clauses.

The sentence begins with a subordinate clause:

• Når først købsdatoen er fundet

After that whole clause, the main clause starts. In Danish main clauses, the finite verb usually comes in second position, so you get:

• ved kunden

instead of:

• kunden ved

So the structure is:

1. subordinate clause first
2. finite verb in the main clause
3. subject after the verb

A simpler example:

• Når han kommer, spiser vi.
• When he comes, we eat.

Not vi spiser after the opening clause, but spiser vi.

Ved is the present tense of vide, which means to know in the sense of knowing a fact.

• at vide = to know
• jeg ved = I know
• kunden ved = the customer knows

This is different from kende, which means to know in the sense of being familiar with a person, place, or thing.

Compare:

• Jeg ved, at butikken er lukket. = I know that the shop is closed.
• Jeg kender butikken. = I know the shop / I’m familiar with the shop.

In your sentence, a fact is being known, so vide is the correct verb.

Reklamationsretten is another compound noun with a definite ending.

It is made from:

• reklamation = complaint / claim about a faulty product
• ret = right
• reklamationsret = the right to complain / right to make a claim
• reklamationsretten = the right to complain / the warranty claim right / the statutory right of complaint

A very important detail: this is not exactly the same as an ordinary commercial warranty. In Danish, reklamationsret usually refers to the legal right to complain about defects within a certain period.

The spelling changes slightly in the compound:

• ret becomes retten in the definite form
• so reklamationsret → reklamationsretten

Here at means that and introduces a subordinate clause.

• ved kunden, at reklamationsretten gælder
• the customer knows that the right of complaint applies

This is very common after verbs like:

• vide = know
• tro = believe
• sige = say
• mene = think

So:

• Jeg ved, at ... = I know that ...
• Hun siger, at ... = She says that ...

Because this is a subordinate clause, and Danish subordinate clauses usually keep the subject before the verb unless something else is affecting the structure.

So you get:

• at reklamationsretten gælder
• literally: that the right of complaint applies

This is different from the main clause inversion seen earlier in ved kunden.

A useful contrast:

• Main clause: Nu gælder reklamationsretten.
• Subordinate clause: ... at reklamationsretten gælder.

So:

• main clause often has verb-second order
• subordinate clause usually has more straightforward subject-verb order

Gælder means applies, is valid, or is in force, depending on context.

So reklamationsretten gælder means:

• the right of complaint applies
• the right is valid
• the right is in effect

This verb is very common in formal and practical Danish, especially with:

• rules
• laws
• rights
• exceptions
• offers
• deadlines

Examples:

• Reglen gælder ikke her. = The rule does not apply here.
• Tilbuddet gælder til fredag. = The offer is valid until Friday.

The commas mark subordinate clauses.

Your sentence has:

1. an initial subordinate clause:
   • Når først købsdatoen er fundet
2. a main clause:
   • ved kunden
3. another subordinate clause introduced by at:
   • at reklamationsretten gælder

So the commas help show the structure clearly.

A note for learners: Danish comma usage has some variation depending on style and whether someone follows traditional comma or new comma rules. In many real texts, you may still often see a comma before at, as in this example.

Yes. The original sentence is correct, but it sounds fairly formal or written. A more everyday version could be something like:

• Når købsdatoen er fundet, ved kunden, at reklamationsretten gælder.
• Når man har fundet købsdatoen, ved kunden, at reklamationsretten gælder.
• Når købsdatoen er kendt, ved kunden, at reklamationsretten gælder.

The original with Når først adds a slightly stronger sense of once that step has been taken.

So the sentence is natural, but it has a somewhat official or explanatory tone, especially because of words like købsdatoen and reklamationsretten.