Install Flash for Chromium on Debian
The package pepperflashplugin-nonfree downloads the Chrome for Linux Debian package (.deb) from Google and extracts the Flash PPAPI plugin (libpepflashplayer.so) to make it available to other browsers system-wide.
The package pepperflashplugin-nonfree is broken since Google changed the method of distribution of the Flash plugin with Chrome 54 for Linux; libpepflashplayer.so is not directly bundled in the Debian package anymore.
This is the reason you have to install Pepper Flash Plugin manually. Download the PAPI version of Flash player from here
sudo update-pepperflashplugin-nonfree --status
You should see somthing like this
Flash Player version installed on this system : 18.104.22.168 Flash Player version available on upstream site: 22.214.171.124