I am developing a flutter application, however I would like a service to be able to run constantly without stopping in order to make an api request every 15 minutes and then send a notification to the user (Android /IOS). I would also like the service to start automatically with the smartphone. I've been stuck on this for more than a week now and I've been browsing the forums looking for a solution but I can't find what I'm looking for. Thank you in advance for any help
You don't do it like that on Android. You cannot count on an application not being killed in the background. Instead, you use JobScheduler or WorkManager to set an alarm and wake you up every so often to perform whatever job you need. These methods can also ensure you're scheduled at startup of the phone.
Also, 15 minutes may or may not happen- Doze mode may cause your app to be delayed and make requests less frequently than that if the phone goes to sleep (although 15 minutes is fairly safe, plus or minus a few).