Temporary VAT reduction by 3% until 31.12.2020

The final acceptance is planned for January 2021, but we pay depending on the construction progress, e.g. after pouring the base, the ceiling, erecting the roof truss, etc., so basically according to the trade.
The service per payment is therefore provided in the 2nd half of the year.
The last payment after handover in January must definitely be calculated with 19%, but the payments in the 2nd half of 2020 should, in my opinion, be taxed at 16% (which is also the case), only the net purchase price must not increase, right?!

So we will also get the future invoices with 16%, but since the house will be finished next year, the differences will then be added. So despite the 16% invoices, we will pay 19% in total. Only those who accept the house between 01.07.20 and 31.12.20 benefit. That is correct, isn’t it?

Why not? By the way, the GU does this relatively cleverly. Otherwise, you would experience the nasty surprise in January 2020 if instead of a 5% final payment (gross), suddenly 10% (from the final payment and VAT back payment) were still outstanding.

Our net purchase price was increased with the argument of the increased costs of our developer (statement came after my inquiry about the increase).

Why does your developer have increased costs in connection with the VAT reduction?