Mixed area / 70% commercial use 30% private use

Hi everyone,
I have been a silent reader for a while now, and since things are getting serious for us, I need your advice.
I own a plot of land located in a mixed-use area. Except for one or two building plots, the mixed-use area is fully developed. There are a few companies, but the majority of the buildings are private residences in the mixed-use area.
Now the building authority came around and said that since we are one of the last, they have to impose a requirement of 70% commercial and 30% private use on us. Nothing about this is stated in the development plan. The community refers to the building authority and vice versa. An inquiry with the building authority only resulted in them saying we should submit a preliminary building request. They cannot give any legally binding information without a preliminary building request, which is clear.
The responsible gentleman at the municipality told us to simply set up an "Ebay shop" or something similar and name the rooms accordingly in the building application so that it looks like a company is moving into the actual residential building. His statement: "A small business license costs you about 20 euros and that should solve the problem."

What do you think about this? How should I proceed?

I was thinking about going to a lawyer and tax advisor to get legally secure advice. I find it a pure waste of money just because the office thinks up such crazy regulations.
Does anyone know a suitable lawyer who could help us / provide information in this situation? I would be very grateful to you.

Strange situation, but if they demand it like that, for whatever reason, I would rather take the small business license for the Zacken than run to a lawyer. At least if that would settle the matter with the building authority. Still, somehow a shady situation in my opinion.

How should I proceed?

Get a small business license and name the rooms accordingly in the building application.

I think it’s pure waste of money.

For the initial consultation, you can operate the small business for 5 years.

just because the authorities think up such crazy regulations.

That is your reasoning. Whether the regulations are crazy can only be judged after reading the development plan and its justification.

Still somehow a shady matter in my opinion.

Nope. Then you shouldn’t buy a property in a mixed-use area. If it is feared that permitting further pure residential use would change the character of the development area, the approval authority risks lawsuits from already established companies and residents.

Thank you both very much.

I did not buy the property but was gifted it by my grandmother.

As already mentioned, the development plan does not say anything about the 70/30 rule; it would have to be amended afterwards for the 70/30 rule to be legally binding.

Then I will probably register the small business and hopefully have peace with it.

it would have to be changed afterwards so that the 70/30 rule is legally binding.

No. It is a mixed-use area. And living and business are supposed to be mixed there. Ideally in a balanced way. And if the mixing ratio threatens to become disproportionate, then nothing may be approved that exacerbates this threat. No additional rule is required for this. The 70/30 is probably based on a ruling by the VGH BW from 9/8/98, in which this mixing ratio was still considered acceptable.

Then I will probably register the small business and hopefully have peace with it.

Just to be safe, ask a local architect who knows the people at the approval authority. The responsible gentleman at the municipality can say a lot when he doesn't have to be modest.