If you can’t use flutterblue connect device with Android Phone. You can try low version Api of Android. These apis are deprecated but worked very well in some Android Phone. These Phones are bad support with new API: you can call the function successful, but scan and connect will be very slow and easy connect fail. To solve this problem, change file: android/src/main/java/com/pauldemarco/flutterblue/
see new file on: https://github.com/mjl0602/fl...
This change didn't solve this problem completely. To solve this problem, must add new args to control the api version. but not use Build.VERSION.SDK_INT. It's works bad.