Window frame defect

Hello,

I have a question.
The window fitter forgot to shorten the frame at the time (see picture).
Now the ETICS has already been glued and only afterwards did I notice it,
the frame was shortened afterwards and since a gap arose,
I had to call the plasterer to stick a piece of perimeter insulation there.

He charged me about €100 for this action.
Now the question, I understand that I don’t have to pay since I didn’t make any mistake.
Who is liable for this, the window fitter? Or should the exterior plasterer have noticed it earlier?

The fact is, I refuse to pay the €100.

Thank you very much in advance

How much are stress, effort, and free time worth to you? More or less than 100 euros?

If there is time, one can make the call or write the letter. That is probably worth 100€. But if nothing comes of it, it was probably a learning experience.

Whoever orders the music pays.

Since we do not know with whom you have concluded which contracts, possibly you are building with a GU or BT - then you do not have the right to summon the craftsmen to the construction site - we cannot give you a definitive answer.

Brief regards