Article 80 establishes transitional rules for supplies occurring around the effective date of the Decree-Law. It stipulates that if consideration is received or an invoice is issued before the law's enforcement, the supply date is deemed the effective date if key events—such as goods transfer, installation completion, or customs declaration—happen afterwards. For contracts concluded pre-enforcement without specific tax clauses, the consideration is treated as inclusive of tax, and the tax must be calculated accordingly. The article defers to the Executive Regulation for detailed implementation provisions and notes its amendment by Federal Decree-Law No. 18 of 2022.