Double costs for the bathroom / who has to pay?

Thank you all for the sobering reality.
I will have to say goodbye to the advance payment.

Stay healthy!

Does it not matter that we couldn’t choose this craftsman ourselves and were assigned him?

Yes, that doesn’t matter.

I will therefore have to say goodbye to the advance payment.

At least you have to pay for the service provided to the person who ultimately delivered it. The others got money for nothing (service not provided) and as mentioned earlier, you can line up with the other creditors there and hope to get a share from the bankruptcy estate. Note: never pay in advance, but only according to progress...

I think everything is clear now?!
There are two contracts, one that you have with the BT
and then you verbally have a contract about the additional equipment with the sanitary installer, which is now bankrupt.
What I don't understand:

after the costs for the standard were "calculated out" with the developer.

Why is the developer charging you?

Is it the case that he billed you the standard amount between you and the sanitary installer? So he paid you or the sanitary installer? Then it makes sense that he (if he now has to provide the equipment again with a new sanitary installer) receives money from you again.
However, you could find a sanitary installer yourself... of course, also pay again. Afterwards. After the service is provided.

Strange situation that the developer apparently prescribed the bathroom companies that you settled with directly.

That is normal. The general contractor or developer makes tenders and thus stays within his fixed price, usually with craftsmen with whom he has had experience. He cannot (and does not want to) change craftsmen weekly.

That is normal. The general contractor or main contractor issues tenders and thus stays within their fixed price, usually with craftsmen they have experience with.

That is clear to me as well. However, this concerns a trade not awarded by the developer, which neither affects their costs, their warranty, nor their scheduling. Nevertheless, they make specifications, which is quite odd.

That is clear to me as well. However, this concerns a trade not awarded by the developer, which neither affects his costs, his warranty, nor his scheduling. Nevertheless, he makes specifications, which is quite odd.

What strange things do you always read into this thread? It is awarded by the developer; the OP only discussed special requests.