Duties of a carport manufacturer

I am surprised that the carport manufacturer does not know the situation and routinely clarifies it. Costs notwithstanding. Very strange.

Maybe because it often happens that the construction company submits the application including the carport

I am also surprised. And: no one has said anything yet about costs, or that I would absolutely refuse to pay them. The company said nothing about costs, but that they did not know if they could even sign it.

Anyone authorized to sign can do that... You have already realized that.

Edit: or did you also pay extra for your house construction so that the architect agrees to put his name on it?

That is actually standard practice. Architectural services need to be paid for, and not just a little.

That is actually standard. Architectural services need to be paid for, and not sparingly.

Correct, but this is also stated in an invoice beforehand.