Android Facebook App Not Working
Edit: this appears to be a problem that Facebook know. It's a concern with the Facebook app, and not a generalised Play Shop concern.
This is what worked for me at the very least.
- Settings > Apps > All > Google Play Shop, Clear data and Clear cache
- Settings > Apps > All > Google Play Provider > Manage area, Clear all information and also Clear cache
It doesn't hurt if you reboot your phone before you try upgrading facebook once again. As well as, the mount was SLOW. Just at least 4-5 minutes. But, it did job. If not try to uninstall it, or simply wait for a fix.