API Warning from google play store when uploading apk

[Munawar Hussain]

Warnings

Your app currently targets API level 28 and must target at least API level 29 to ensure it is built on the latest APIs optimized for security and performance.

From August 2020, new apps must target at least Android 10 (API level 29).
From November 2020, app updates must target Android 10 (API level 29).

Tip: Change your app's target API level. Learn how.

[Symbroson]

the not yet released beta docs contain a FileStructure section which contains a description of the build.json file as well. have a look:

https://alex-symbroson.github.io/Docs/docs/intro/07FileStructure.htm#build.json

[Steve Garman]

The current version of DroidScript does not yet target API 29.
The update to DS has been delayed by events beyond our control.

We hope to provide an API 29 update in the next couple of weeks.

In the meantime I recommend leaving updates to your app targeting API 28

For those wishing to experiment with raising the target of their app using a build.json file, if your app does not already have a build.json, I recommend using the minimal version pasted below.
This is not guaranteed to make apps built with current release or beta work at API29 faultlessly.

{
"manifest": {
"targetSdkVersion": 29
}
}