When I installed zoom the other day I had an error message “Duplicate target”. This has happened also with other applications. Pacman finds two pkg.tar.xz files and is confused.
When errors occur, go to your /tmp folder and check what is happening.
When you installed it with packer you will find a folder there with the same name. The same applies to trizen and yaourt. And try to figure out what is going wrong.
In my case I had two files. One was the original file and the other was the one coming from the build (PKGBUILD).
Double click the correct file or install with
sudo pacman -U ....pkg.tar.xz
Sometimes we run out of space in the /TMP
Sometimes if the build is becoming too big you can run out of place. Tmp is too small or similar message shows up.
This is the solution and there is no need to reboot. More info on Arch Wiki.
mount -o remount,size=4G,noatime /tmp