dbNotify mobile application requires Oracle REST Data Services (ORDS) to communicate with your Oracle database. ORDS is preconfigured and available with all Oracle Autonomous Database instances, you just need to enable it. You can use Oracle Application Express (APEX) to enable and manage RESTful Web Services, and probably this is the easiest way. Oracle APEX also comes preconfigured and available with all Oracle Autonomous Database instances, on Autonomous Database Details page, under Tools section.
Please visit the page https://oraclexp.com/ords/f?p=OEM:dbnotify for instructions.