The insurance company (or payer) is indicating that they want a prior authorization going out on the claim. There are a couple of ways to get a prior authorization on the claim form in Therabill. There is the simple way and then there is the more powerful method called Authorization Watch. Descriptions of each are linked to below. Once you have entered the authorization, you can then go ahead and resubmit your claim (this can easily be done from the error page by clicking the Resubmit Electronically button at the top of the error page.
Authorization Watch: https://therabill.zendesk.com/entries/24115436-Authorization-Watch