You my run into this problems after a fresh install of i3wm. If you are a noob like me this may help.
Multimedia Keys not working.
Make sure you have installed: playerctl before adding anything to your config file.
Issues with screenshots, install: flameshot.
After isntall you got to see the icon at your bar.
If it doesnt appear :
Search for : tray_output primary in your config file and comment it : # tray_output primary
Mod+Shift+R and the icon should appear.