If it turns out in the course of the ongoing construction procedure that the advance payment was set too low, the client can in principle demand an advance payment. However, he must then provide sufficient evidence to show why a higher advance payment is necessary.
The client cannot demand an advance on costs if he does not want to or cannot remedy the defects. This applies, for example, if he has sold the building in the meantime. He can also no longer demand an advance payment if the defects have long since been remedied.