What is the legal basis?

What is the legal basis in Austria?

§ 16. Change in the assessment basis

(1) If the assessment basis for taxable turnover has changed within the meaningof Section 1 (1) lines 1 and 2, then

1. the entrepreneur who carried out this turnover, the amount of tax owed for it, and
2. the entrepreneur, to whom this turnover has been made, to correct the input tax 

deduction used for this. The corrections must be made for the assessment period in which the change in remuneration occurred.

(3) Paragraph 1 applies mutatis mutandis if

1.the fee for a taxable delivery or other service has become uncollectible.

What is the legal basis in Germany?

Section 5: Taxation

§ 17 Change in the taxable amount

(1) If the taxable amount for a taxable transaction, within the meaning of § 1 paragraph 1 number 1, has changed, the taxable person who executed this transaction must adjust the respective VAT amount due.

(2) Paragraph 1 shall apply accordingly, if the agreed consideration for a taxable supply of goods and services or a taxable intra-Community acquisition has become uncollectible. In the event that the consideration is subsequently received, the VAT amount and the input VAT deduction are to be readjusted;