Prepayment at the door, when paying after construction progress?

Hello dear ones!
Our construction company is currently building the shell of the house.
So far, we have always paid according to the construction progress.
Now an invoice has arrived for the front door (which has not yet been installed or even present).
The construction company said that they are quite allowed to collect payment for additional services in advance.
Is that normal?
What would happen if one of the additional services (door, tiles, etc.) turned out to be defective in the end and no one is found responsible?

This is my first house, please excuse any stupid questions on my part.

I would avoid prepayment. What have you contractually agreed on?

I find a deposit still acceptable - after all, for example, windows and front doors are made individually for you. Full prepayment is out of the question - unless you have arranged it contractually.

Hello,

Our construction company is currently building the shell. So far, we have always paid according to the construction progress. Now an invoice has come in for the front door (which has not yet been installed or even present). The construction company said that they are allowed to collect additional services in advance.
Is that normal?
What if one of the additional services (door, tiles, etc.) turns out to be defective in the end and no one is found responsible?

No, that is not normal, but it is a well-known trick to circumvent the payment schedule!

Even if you ordered a custom-made front door, which usually requires an additional charge, this should – hopefully – have been agreed upon in writing via an addendum to the contract. This additional charge is then distributed proportionally across all due interim payments from the moment the special door was purchased.

So do not pay in advance and refer to the valid work and payment schedule.

Rhenish regards