Article 137 addresses the administrative duties of a closing business. If an enterprise or permanent establishment ceases its activities, it must notify the Tax Authority within seven days of the cessation. The taxpayer is then obligated to file a final tax return by the specific deadline set by the Authority in a formal notice. Any tax due based on this final return must be paid on that same date. This accelerated timeline ensures that the state can collect outstanding taxes promptly before the entity completely winds down its Omani presence.