ᐅ Mold on wood/structural frame—Is it possible to withhold payment from the progress invoice?

Hello,

our shell construction has been completed since December, and the windows are currently covered only with protective film.
Since we have a flat roof, there is the possibility to convert the attic later on.
Therefore, the ceiling above the staircase was closed off with a wooden structure.
The vapor barrier and the flat roof have been completed.

No interior walls and nothing plastered yet. For 2 months, there was still water standing in the basement up to 5cm (2 inches).
Because the windows are covered with film, there was heavy condensation inside during December and January.
Now I have noticed that mold spores are appearing around the roof hatch.
Just yesterday, the second interim invoice arrived, which should be paid within the next 10 days.
That’s 150,000 euros. The first payment was 140,000 euros (there are 7 in total).

Can I deduct something from the invoice amount and demand that the defect be fixed before I pay?
We are building a turnkey house.
Should I get an independent expert to assess the situation?
What do you think?

In my neighbor’s semi-detached house, the mold infestation is even worse...

Thanks for your help.

Here are some pictures

Sorry that the images are rotated

Sorry for the off-topic comment:
You are paying €290,000 for a structure that isn’t even fully enclosed yet (no windows installed)?

What is the total project cost? €800,000?

If not, these figures seem completely disproportionate.

You should involve an independent expert with such an investment anyway. For example, take a look at the Bauherren-Schutzbund.

The land alone already cost 145,000 and is included in the total of 290,000. So it’s not that bad, right?