Advance payment for the window installment

Our general contractor informed us that the window manufacturer is offering a discount and wants to pass it on to us. This discount only applies to orders confirmed and paid for before the end of this month.
We are still far from the phase of installing the windows (we are just starting).

That a general contractor passes on such information to his customer is suspiciously unusual. The insolvency issue has already been mentioned repeatedly; given this, are you seriously proceeding without a completion guarantee?

Should I ask the general contractor/window manufacturer to have their bank issue such a surety bond?

Are you seriously building without a completion guarantee given the same?

Unfortunately, this is the first time I am hearing about this completion guarantee.

Is it a big main contractor, or a small one? You mentioned "she" a few times, is it a single woman? Or a larger company? And is it really a main contractor, or are you building with a construction company (turnkey?) on an existing plot? If you really fear or consider the company's insolvency plausible, I would not make an advance payment. You are transferring money to your construction company, not to the window manufacturer. If they declare insolvency shortly afterward, you will have neither money nor windows.

Is it a large general contractor or a small one? You mentioned "she" a few times, is it a single woman? Or a larger company?

It is a small family business. The owner and contact person is the lady I am addressing.

And is it really a general contractor, or are you building with a construction company (turnkey?) on an existing plot?

I think in our case it is a general contractor. We purchased the land ourselves and then commissioned them to build the house.

If you really fear the company going bankrupt / consider it plausible, then I wouldn’t make advance payments.

No, not really. Nothing special that worries me. Every time I visit the construction site, I meet craftsmen and see how the work progresses.
It is just the general risk that can happen to any general contractor.

You are transferring money to your construction company, not the window manufacturer. If the latter files for insolvency shortly thereafter, you have neither money nor windows.

That is actually a bit confusing. I pay the money to the general contractor, who then pays the window dealer.
If the window dealer goes bankrupt, the general contractor should still be liable to me with their own money, right?
If I apply for this surety bond, should the general contractor provide it to me or to the window dealer?

I would have fewer concerns about Drutex going into insider mode. They are already quite large. Although, of course, these days you should never say never. I was more concerned about your family-owned general contractor. Of course, none of us can assess how financially stable they are. Maybe I watched one too many episodes of "Botched Construction." But your general contractor probably won't pay for these windows before they are delivered (or is that explicitly stated in the offer conditions?), so I wonder why your general contractor wants the money in advance. Roughly, what amount are we even talking about? I think our window installment invoice (also Drutex) was over €40,000.

Please observe § 632a of the Building Code "Progress Payments" and § 650m of the Building Code "Progress Payments; Securing the Claim for Payment", so pay a maximum of 90% of the requested payment. What was agreed upon in the construction contract? That should be called "payment based on construction progress", right? Your general contractor is liable for what was contractually guaranteed in the description of construction services or in the construction contract (fixed price? price adjustment clauses or similar?).