Are you able to test this on another device? If you don't have another mobile device, ask a family member or friend if you can temporarily log into your Facebook account on their app and see if notifications come through there. If they don't, then it could be an issue with your account -- I've seen a few posts on this forum from members with this odd issue of their specific Facebook account not generating notifications, regardless of the device they're logged into (while others who log in on that same phone do get notifications). These users have checked their Facebook notification settings in the account (using a computer browser), which show all notifications turned on. I haven't seen a definitive fix for this, and I usually recommend contacting Facebook support about it.