Twilio Lookup API is a tool that helps businesses stay compliant with the Telephone Consumer Protection Act (TCPA) by checking if a phone number has been reassigned. This feature is useful for marketing notifications and can improve contact rates, increase campaign efficiency, and avoid compliance fines. To use the Lookup API, users need to have a Twilio account and test credentials. The API requires two parameters: Fields (reassigned_number) and LastVerifiedDate. The response includes information about whether the number has been reassigned or not, as well as other data packages. Twilio uses the official FCC database for updates and encourages users to refresh their database starting on the 17th of each month. Debugging common error codes is also discussed in the text.