The contractor wants to issue an invoice for planning services

Thank you for your lively discussion in this thread.

The draft created by the GU for us served as the basis for creating the offer. It has to have some basis for the offer creation (which house size, how many windows, do we want 5 bathrooms or only 1, etc. etc.). Therefore, I do not consider the drafts to be independent; we also do not use them further, and in our view, they were not yet mature enough for us to go to another GU with them saying "Now build me this, please." The first draft was created based on our sketch/room ideas, but unfortunately the house was then almost 175 sqm – too big for us and it would certainly have become too expensive. Therefore, we asked for a reduction, created an exact sketch with measurements of how big each room should be. Based on this, the draft was reduced. This "reduced" draft then served as the basis for the created offer. Just to explain the draft story.

I am happy to keep you updated. However, when there will be a clear conclusion, I consider that to be open.

What exactly was agreed upon at the end? In the initial post, you write about an offer from the contractor. Was this accepted despite incorrect description and planning? If not, no contract was concluded and thus no payment obligation. The expenses of the general contractor are offer costs, as the client and contractor had not yet agreed on the contract content.

I quote myself. The inquiry was answered with no. So everything is clear. The general contractor has no claim for compensation. It might look different with an architect. If the general contractor issues an invoice, please let us know on what basis it is founded.

I fully agree with and while I understand the general other views in principle, I do not for this case.

I want to build and say "please make me an offer for a single-family house with 150m2 and kfw55 standard".
The general contractor makes an offer for a single-family house with 170m2 and energy saving ordinance standard... aha. It's logical here to say, I wanted an offer for something else!? And according to some here, this change to the originally requested offer should then cost a fee?

Then you could start a new business model, I intentionally always offer something different than requested and then charge for the change to the actually requested offer upon inquiry... clever.

No, with the explanation it is clear.
In the initial post, however, it sounded as if the following process might have been possible:
"I need a house with the rooms blabla, how would it look with you?"
1. Offer with draft - "No, I don’t like the draft, please smaller and here and there different"
2. Offer with first adjusted draft - "Well, this and that is fine but please draw here and there differently"
2. adjusted draft - "Better, but can you make the window bigger and the stairs to the left, oh then the upper floor doesn’t fit anymore but please make an adjustment."
3. adjusted draft etc. etc.

Obviously, the contractor should have been straightforward somewhere, but on the other hand, you can’t naively think that this was all still just business initiation.

Now that it is clear the process was much more streamlined, I also believe there is no claim and would, if I were the OP, object once and then just wait it out.

No, with the explanation it is clear. But in the initial post it sounded as if the following process might have been possible: "I need a house with the rooms blah blah, how would that look with you?" 1. Offer with draft - "No, I don't like the draft, please smaller and a bit different here and there" 2. Offer with first adjusted draft - "Well, this and that is fine but please draw this and that differently" 2. adjusted draft - "Better, but can the window be bigger and the stairs moved to the left, oh then the upper floor no longer fits but please make an adjustment." 3. adjusted draft etc. etc. Clearly the contractor should have spoken frankly somewhere along the way, but on the other hand one cannot naively think it was all still just business initiation. Now that it is clear the process was much tighter, I also believe there is no claim and in the position of the OP I would object once and then just wait it out.

The OP never accepted the offer at any time. Therefore, there is no contract. This is called "work without a contract" in professional circles. It follows that there is no claim for payment. It is completely irrelevant how many rounds of negotiations there were.

The offer was also for the house construction. For the theoretical case, which does not actually apply, one could have argued that there were several planning contracts. Almost an order without an offer. Then Nordanney's findings are decisive. Although perhaps shaky again, if, for example, the mentioned entrepreneur was also the architect? But that is now pointless, the present case is different.