In the case of input tax amounts that are related both to unauthorised tax-exempt and other sales, a distribution standard must be selected which leads to the most appropriate result in individual cases. The law does not prescribe a certain procedure. Any method which ensures an economically correct assignment of the input tax amounts is permissible. If the basis for a proper, exact allocation of these mixed input tax amounts according to § 12 para. 4 UstG [Sales Tax Act] is lacking , it has to be estimated. The distribution does not have to be based on the turnover key if this does not lead to a result that is as appropriate as possible (Administrative Court 31.1.2018, Ra 2016/15/0001).