Heat pump promotion - Wrong invoice uploaded

I do not know the procedure of BAFA in detail. However, I am not completely uninformed on the topic. If you have been granted a subsidy by promise/notification, there are legal regulations for the approval and payment (BHO or LHO). The payment is regularly associated with the verification of proper use (or other names). The approval by promise/notification is always granted under the reservation of the final review. Now you have somehow submitted a faulty invoice and the subsidy was finally reduced. So far, everything is according to law and regulation. Unfortunately, from the information you have provided so far, we do not know why BAFA did not recognize your invoice (tiler). If the invoice is faulty (google requirements for invoice), then request a new invoice from the tiler. In your previous final letter, there is also information on legal recourse or similar. These are usually 30 days. During this time, you can file an objection against the verification of proper use. With your objection, you submit the new invoice. Then a renewed review of this point begins. Everything else is generally not reviewed again. Your fear is unfounded. Perhaps with the invoice you also violated formal requirements of the guideline. An example would be cash payment. In such cases, you can forget about the objection.

Strictly speaking, you would now have to submit the corrected invoice and repay the portion of the subsidy that was overpaid.

A repayment will not be necessary. With almost all subsidies, the "reimbursement principle" is applied. So first the BAFA customer has to pay their craftsmen or contractors, then they can claim their expended costs proportionally by means of invoice and proof of payment (bank statement).

You did not read the text carefully! An incorrect (too HIGH invoice) was submitted. It was erroneously reimbursed. The correct invoice from the tiler would be 4000€ lower! So (from the BAFA's perspective) false information was provided that would lead to a (partial?) repayment if discovered. The OP is worried that the entire measure might become "ineffective" and that he would have to pay everything back. And/or he honestly wants to correct the mistake without risking the entire subsidy amount.

You did not read the text carefully! A wrong (too HIGH invoice) was submitted. It was mistakenly reimbursed. The correct invoice from the tiler would be €4000 lower! So (from BAFA's perspective) false information was provided that would lead to a (partial?) repayment if discovered. The OP is worried that possibly the entire measure would become "ineffective" and he would have to pay everything back. And/or he honestly wants to correct the mistake without risking the entire subsidy amount.

Yes, I did not read the last sentence in the first text correctly. Sorry! I would implement the repayment of the unjustified part and explain the facts. In my opinion, this behavior will not lead to the repayment of the entire subsidy.