When you log in to EVA for the first time, it will need to be authenticated by Frontier. This is to make sure your account details are kept safe.

Frontier will email you with a five-letter code which you need to type into EVA before Frontier will send out any more information. Each authentication code is only usable once, and matches only one login attempt. This means that if you log in twice without authenticating, the first authentication code you receive will no longer work. The codes can take a few minutes to arrive, so if you log in again during that time then you must wait for the second code to arrive.

If you want to make sure that you're using the right code, the easiest way is to just wait a couple of minutes to check that a second code doesn't arrive.