When trying to add the recommended items using B4A SDK Manager I am getting this type of error after an item has been added:
Example of error:SDK Error said:1. Open Tools - B4A Sdk manager.
2. Install all recommended items. This will make the switch to AndroidX. You can always go back to the previous SDK.
Loading package information... Loading local repository... Info: Parsing C:\Android-SDK\build-tools\27.0.1\package.xml
Info: Parsing C:\Android-SDK\emulator\package.xml
Info: Parsing C:\Android-SDK\extras\google\usb_driver\package.xml
Info: Parsing C:\Android-SDK\extras\intel\Hardware_Accelerated_Execution_Manager\package.xml
Info: Parsing C:\Android-SDK\patcher\v4\package.xml
Info: Parsing C:\Android-SDK\platform-tools\package.xml
Info: Parsing C:\Android-SDK\platforms\android-28\package.xml
Info: Parsing C:\Android-SDK\tools\package.xml
....
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Unzipping... android-9/dx.bat
Info: "Install Android SDK Build-Tools 28.0.3 (revision: 28.0.3)" complete.
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WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.sun.xml.bind.v2.runtime.reflect.opt.Injector$1 (file:/C:/Android-SDK/tools/bin/jaxb-impl-2.1.jar) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int)
WARNING: Please consider reporting this to the maintainers of com.sun.xml.bind.v2.runtime.reflect.opt.Injector$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release