I have a handheld POS terminal with a custom ICBC android 5.1.1 "TERMINAL VERSION" installed. A lot is missing in the version, tapping "about terminal", then "build number" shows a page but the "developer mode" option is missing. the ADB is off as well. Side loading apps using OTG results in the "App not installed" error. What can i do to get to developer mode or turn on adb or install apps?