Stairs delivered without a railing and now I have to pay extra?

No, it says "Handrail (this ends at the newel post)". Nothing about railing ...

Somehow I still have problems understanding

The contract literally says:

"Included in the standard delivery scope are the necessary stair railings with handrail (this ends at the landing post), all required fastening materials, and a surface treatment (colorless)."

But the employee told me that the railing meant the railing on the stairs, on which the handrail then rests.

But now the company says that I did not order a railing for the stairwell (i.e., around the stairs) and now I have to buy it additionally, since I didn't order it (almost 2,000 euros)

For me, the stairwell is the inner curve, and the outer curve is often next to a wall where a handrail might be attached. But normally no railing is installed there, unless the staircase is freestanding. What kind of staircase do you have? Is it completely freestanding?

Maybe post a picture or mark the missing railing on a floor plan.

Attached is the architect's plan. It even says railing on it. But now I have to buy that separately.

As I understand it (Achtung, Laienmeinung!), the construction company is right. However, they should have informed you that additional costs would arise.

Best regards
Dirk Grafe

Now I understand. According to the construction service description, it is actually not included and should have been noticed during the review of the construction service description. However, if the drawing is part of the contract for work, then, in my opinion, that would be an argument. Do you have an expert at hand who can throw a few paragraphs at the construction company regarding fall protection? Maybe a compromise can be reached somewhere in between. But this is once again a very good example for future builders of what may not be included.

...ends at the support post!

That is then a clear statement in the construction performance description