The current implementation utilizes the NotificationChannel, which was added in API Level 26. If you want to target lower API Levels, take a look at the older implementation Alarm Manager Implementation. Have in mind, that this approaches is not supported with API Level 26 or newer due to limitations in the OS.
So, how can I implement background services that will work on both API Level 26+ and below? Because the two solutions provided will only work on either 26+ or below 26.
As stated in the README:
So, how can I implement background services that will work on both API Level 26+ and below? Because the two solutions provided will only work on either 26+ or below 26.