Article 220
Every taxable person shall ensure that, in respect of the following, an invoice is issued, either by himself or by his customer or, in his name and on his behalf, by a third party: (1) supplies of goods or services which he has made to another taxable person or to a non-taxable legal person; (2) supplies of goods as referred to in Article 33; (3) supplies of goods carried out in accordance with the conditions specified in Article 138; (4) any payment on account made to him before one of the supplies of goods referred to in points (1), (2) and (3) was carried out; (5) any payment on account made to him by another taxable person or non-taxable legal person before the provision of services was completed.