REVENUE MEMORANDUM CIRCULAR NO. 13-2021 issued on January 27, 2021 announces the availability of the BIR Mobile Taxpayer Identification Number  (TIN) Verifier Application, also known as the “BIR Mobile TIN Verifier App.” Said app is available for download on both the App Store (for iOS) and Google Play Store (for Android).                                                                                                              The BIR Mobile TIN Verifier App is a service channel for taxpayers to send online TIN validation and TIN inquiry using their mobile phones with real time response from the concerned BIR office.                  The Revenue District Offices (RDOs) shall inform taxpayers to download and use the said App for TIN validation or TIN inquiry transactions. Acceptance of walk-in taxpayers to get the service shall still be available in all RDOs to serve taxpayers with no access to the said mobile service app.