Sorry if this is too basic but have you deleted the cache and force-closed the app before trying again? Or even the storage, if you don't have any other accounts on it to worry about.

If you don't know what all that means, then I suggest uninstalling the app (if you don't have any other accounts on it), rebooting your phone, and then reinstalling the app to try again. It's overkill, but should offer the best chance of working unless somehow that connection is being blocked by something strange and more specific to you.