Article 56 establishes the framework for tax invoices, granting each Member State authority to determine their specific contents and issuance deadlines. This is subject to minimum details mandated by the GCC Ministerial Committee. Member States are also permitted to allow for simplified invoices under locally determined conditions and rules. A key provision addresses currency, allowing invoices to be issued in any currency, provided the final tax value is stated in the currency of the Member State where the supply occurred. The conversion must use the official exchange rate effective on the tax due date.