Before the last installment, how should one behave correctly?

Post a picture of the problem, then at least people will know what is being talked about here.

If you pay out everything, then you have no leverage left.

The staircase was planned appropriately according to the drawing, but presumably because it was more convenient, the stair builder made the steps longer than in the drawing without consultation. As a result, the DIN clearance height is not maintained; this would have to be constructed, which I cannot show in the photo.

What kind of deviation are we talking about? 1cm or 10cm? Unfortunately, you can’t quite imagine the whole thing yet, where the clearance height is not observed. Which staircase is it about, and is it about the clearance height to the floor slab?

But with a significant deviation, if you have agreed on it with your wife, you should withhold something. If you pay in full, all leverage is gone. But what is crucial is also how big the deviation is and how it could be corrected accordingly to determine the withholding.

As it sounds, it's about millimeters...

How large are the tolerances according to the DIN downwards when >=200cm is required?