Can't login to Facebook App

I’ve found

that I’m not able to log in to the Facebook app on my iPhone 6S, software

version 12.4.1.

I have turned

my phone off and then on again, I have deleted the app and reinstalled it, and

as a last resort I reset the network settings on my phone. None of these

attempts resolved the issue.

I am able

to successfully log in to Facebook on Safari.