goodday to you all, people are complaining of not
being able to install apps on their Android device,
and it always display ‘apps not installed ’ or ‘
error encountered while trying to install app’ in
the process of re-install an app on your device.

the most common causes of this error are:

==>Corrupted phone storage / SD card: This is
the most common cause of this error.
==>Insufficient storage space:
==>Corrupted app (apk file):
==>Permission error: The Android phone might be
going through a permission crisis.
==>Temporary OS glitch: The Android OS might
have encountered a minor error.
==>Apk signed certificate clash: Trying to install
another version of an app (with a different signed
certificate) on the same phone will result in this
error.
==>Installing an unsigned apk: Trying to install an
unsigned apk could result in this error.
==>Wrong app installation location: Some apps
will only be successfully installed on phone
memory while others can be installed on both
phone memory and SD card. Trying to install the
former on SD card could result in this error.
==>Installing on a mounted SD card:
==>Unacceptable apk name: Renaming some apk
files prior to installation has been known to result
in this error

Two method to Fix Application Not Installed on
Android Phone

I’ll show you two simple ways to fix this.

METHOD ONE
=> Get your phone rooted (comment below for
aid)
=> Download any file explorer app with root
access from playstore or download solid explorer
and unlocker now.
=> Install the app(s) to your phone and launch.
=>For solid explorer , go to settings, click on files,
scroll down and check "Back goes to root" .
=>Click back untill you reach system root and
click on the folder, "data".
=> Solid explorer will ask for root permission,
please grant it.
=> When the next window opens, look for the
folder, data and open it.
=> Now, you will see a list of folders (system
folders of all the installed apps in your phone).
=> Look for the one that has the name or
company name of your missing app and delete it.
For eg. zarchiver is ru.zdevs.zarchiver .
=>You can now re-install the app with no hassle.

NOTE: Please, be careful of how you access your system folders. You might mistakenly tamper with important folders which leads to phone malfunction. It's advisable not to access it all,.unless you are aware of your intention and
actions.

METHOD TWO
If the first method didn’t work out for you, then
factory reset your phone and everything will be
back to normal. Before you factory reset, back up
all your files to SD card and remove the SD card
from your phone.

source: www.niyonice.com/2015/03/2-methods-to-fix-app-not-installed-on.html?m=1