Article 13 provides a critical clarification for taxpayers who have received official permission under Article 12 to use an accounting method other than the accrual basis (such as the cash basis). In such instances, any legal reference to 'expenses incurred' during a tax year must be interpreted specifically as a reference to amounts that were actually paid out during that year. This rule ensures that the timing of tax deductions aligns correctly with the alternative accounting method authorised by the Authority, preventing discrepancies between recorded expenses and actual cash outflows.