Board Thread:Questions and Answers/@comment-30592875-20161125025833/@comment-28150993-20161125142456

You have run out of request token. You can get more from doing expedition, complete missions, or get them as resources from certain maps.

The FAQ page Pandacath linked has pretty much all the message-alerts in-game, so whenever there's an alert you're unfamiliar with, you can check there.