Energy Performance Certificate - What documents are required?

Good day dear community,
as I have often written, we are currently building and are happy to soon have our own home.
A semi-detached house with 148 sqm in KfW55 standard is being built.

According to the builder, we are allowed to carry out our trades ourselves. In other words: to look for the appropriate craftsmen ourselves.
Now we have done this three times and the builder was not pleased about it. No idea if they receive a commission or something similar, but we save a lot of money! The differences amount to between €2000 - €4000 compared to the builder's craftsmen.
It was also noticed that we are being quite pressured.
Our trades in self-performance were all within the builder's process.
Now I am asking myself which documents are needed for an energy certificate..?
It is clear that the U-values of the windows and the insulation play a major role.
These have been submitted, including a specialist contractor declaration from the craftsman.

Now my builder or supposedly the structural engineer wants an invoice as well as the order from our own trades.

Is that normal??? Why do they care at all?
They want to see the figures openly on the table. That's what the builder tells me.

Can you tell me if this is usual? Are there different stages of verification?

*in the construction window of the developer

I have no experience with this, but if his "excuse" is that he needs the exact items installed for the energy certificate based on the invoice, then just send an invoice with the amounts blacked out. That won't satisfy his curiosity at all, and he doesn't need to know what you paid for the certificate. I think he's more annoyed that you outsourced it and he missed out on money.

Yes, there are "different stages of the review." For the building application, the preliminary thermal insulation certificate, which is based on assumed materials, is submitted. At the end of the construction, the thermal insulation certificate is corrected with actual figures, if necessary. The creator must be able to verify what was installed. Whether an invoice has to be disclosed for this ... it is certainly the most convenient way for everyone. As an alternative, explanations from the individual trades come to mind with the naming of the building materials and their properties. Or you black out the amounts on the invoice.