Occurred or perfected the taxable and born, consequently, the tax obligation shall be: 1. in the sale of personal property: b) in all cases other than those referred to in the previous paragraph (sales to public entities) 4, when issued the invoice or equivalent document that leave evidence of the operation or the price is paid or Since the actual goods delivery, is made depending on whichever comes first. Omissis 3. In the provision of services: omissis e) in all cases other than those mentioned in previous literals (public services and telecommunications, other services of successive tract, services provided to public entities and services from abroad) 5, when issuing invoices or equivalent documents by who provides the service, runs the provision, is paid, or the consideration becomes due, or be delivered or put at the disposal of the purchaser the good that would have been the service object, depending on whichever comes first. Considering the above, we can conclude then that our legislator presents four possible situations that make birth the tax liability on the sale of movable property and or provision of services to non-governmental entities, the first one, is the issuance of the invoice, which clearly should be the source of the obligation by excellence both and inasmuch constitutes a document containing the information necessary to determine the tribute. Secondly the norm makes mention to the issuance of an equivalent to the invoice document however does not define what are these documents, we could say that a document equivalent to the invoice could be a delivery note which is ruled out by virtue that this document implies necessarily the delivery of goods which is in itself a source of obligation; We could also talk about the order of shopping, which brings together the elements necessary for the determination of the tribute, amen to be obligatory for the parties contract, however the issuance of this depends on the buyer and not the seller, being the source of the tribute is to sell and no purchase is then excluded; another document used by some companies, is the Pre-factura, which undoubtedly meets all the requirements necessary to make birth the obligation and to determine the tribute, however is not a document of widespread use, and use much less than mandatory.