Unable to Login using Facebook on iOS
Changed Facebook Credentials:
If you have changed the ID or password while updating the app, then Facebook cannot recognize the credentials. The only solution to this problem is to replace the credentials to the old ones, uninstall the app from your idevice and then reinstall Facebook .
Insert Correct Credential:
Make sure that all the credentials you entered to log in to your Facebook account are correct. You can open any browser and check the Username and password. If your password is wrong, then try to retrieve them by clicking on 'Forget Password' tab.
Uninstall and Reinstall:
The most common solution to the problem is to uninstall it from your iPhone or iPad and then go to the AppleStore and search for Facebook for iPhone and then download and reinstall it. Hopefully, the updated version will work smoothly on your device.
Use Username instead of Email:
If you can't login to your Facebook account on your iOS device, then open your Facebook account from your laptop or desktop. Then go to Account Setting and replace the email address with the username. Now you restart the app on your iPhone or iPad and put the username instead of email and password and login to your Facebook account.
Open Facebook from any browser of your choice and sign in. Then go to the Facebook settings and then select the Security tab. Now you need to remove the iOS devices from the list. Also, you have to go to the Settings of your iPhone or iPad and then go to the Privacy section. In the Privacy section, you need to disable Facebook. Now try to log in from your Facebook app on your iDevices.
The final solutions to resolve the problem
1. On your iOS device, go to Settings>
2. Log in to Facebook from your computer and then go to Settings>
3. Now open your device go to Setting>General>Reset
4. Now click on the 'Reset Location and Privacy' and confirm
Now open your Facebook account from the app on your iOS device and enjoy.
Read more: https://www.supportforhelp.com/