1) Make sure you don’t have a two-step verification. Two-step authorization is not currently supported. 

If you have 2-steps authorization, please enter your program in this form. We will do our best to support it in the future.

2) Try logging in with the credentials you use on the airline website. If you are able to do it there, but not within the app, please send feedback from the app's settings to give our Support Team a heads-up.

3) If you see an Unknown error (or any other error type) try to refresh the page, and then check it again for the new status. Or, try to delete and add it again. See here how you can do it.