Article 21 grants the Tax Authority broad powers to request information from any person who has earned income subject to Oman tax, or from those holding information regarding another person's tax liability. The request can include full details of the income, identity, and address of the recipient, and any other relevant data. The person receiving the notice must respond within the specific timeframe designated by the Authority. This Article is a primary tool for tax discovery, allowing the Authority to identify taxable events and verify the accuracy of third-party income reporting.