Help How to make a system app on Android 9

[Natsuki]

I develop a custom tablet used Android 9.

I've tried to build a system app into '/system/priv-app', but after the device startup is completed, it automatically shuts down and transitions to the "Android Recovery" screen.

what do I have to do to get my device to boot successfully?

my system app is same as that shown on the following website,
and fixed a mk below.

https://devarea.com/aosp-creating-a-system-service/

・SampServiceApp/Android.mk
-------------
# LOCAL_SDK_VERSION := current
LOCAL_PRIVATE_PLATFORM_APIS := true
-------------
added "LOCAL_PRIVATE_PLATFORM_APIS" insted of "LOCAL_SDK_VERSION" for successful compilation.

and also, this app probably doesn't need any permissions with whitelist.
I run 'development/tools/privapp_permissions/privapp_permissions.py', but the results is empty like this.
---------
<?xml version="1.0" encoding="utf-8"?>
<permissions>
</permissions>
---------
https://source.android.com/devices/tech/config/perms-whitelist

Thank you in advance for your support.
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