Learn Hardcore German: Ich mache Zusatzkosten geltend, denn ich habe die Belege. - I claim additional costs, for I have the receipts.

Because geltend machen is a fixed verbal expression, and in a main clause the conjugated verb machen goes to the second position, while geltend stays at the end.

So:

Ich mache ... geltend.
not Ich geltend mache ...

This works a lot like a separable verb, even though geltend machen is usually treated as a verb + adjective expression.

Compare:

Ich mache die Kosten geltend.
Er macht seine Ansprüche geltend.

In a subordinate clause, the whole verbal part moves to the end:

..., weil ich Zusatzkosten geltend mache.

What exactly does geltend machen mean?

Geltend machen is a common formal expression meaning something like:

to claim
to assert
to invoke
to make a claim for

In this sentence, it means the speaker is officially claiming or submitting additional costs.

It is often used in formal, legal, insurance, or administrative contexts, for example with:

Kosten geltend machen = to claim costs/expenses
Ansprüche geltend machen = to assert claims/rights
Schadensersatz geltend machen = to claim damages

So this is not casual everyday phrasing; it sounds fairly formal.

What is Zusatzkosten grammatically? Why is it written as one word?