Can't connect with IPhone-app

[TangoSmurfen]

I can logon and use Duolingo from my computer.
I can logon but not use Duolingo from my IPhone, using the IPhone-app.
These used to work.

When I choose an excersice I got the message: Can't connect to Duolingo

[WikiCopter]

Make sure you have internet connection, close and reopen app, logout and login?

[TangoSmurfen]

I have an internet connection.
I have tried to close, reopen
I have tried to logout, login
I have tried to unistall, install the app
Still it does not work