I downloaded a couple of APK's (on page 6 of this thread) but they refuse to install - no error message but "App not installed"
I got the same Problem some days ago.
Maybe you have to change the "device_provisioned" from "0" to "1" with SetEdit. For this you need to install the Database Editor on FireHD and change the write permission by your PC/Notebook.
https://m.apkpure.com/settings-database-editor/by4a.setedit22
1. Download and install Settings Database Editor on the Fire tablet (Sideload).
2. Plug your tablet into your PC and open an ADB window. (USB Debugging on)
3. Download ADB platform-tools on you PC (C:\platform-tools)
https://developer.android.com/studio/releases/platform-tools
4. Open CMD on the PC and enter the follwowing:
adb devices
The Tablet asks for access!
Now type:
adb shell pm grant by4a.setedit22 android.permission.WRITE_SECURE_SETTINGS
Disconnect Tablet from PC.
Navigate to the Settings Database Editor on your tablet.
Select “Global table” from the top right menu
Find “device_provisioned” = 0
Change the value to “device_provisioned” = 1
Reboot your tablet.