This error occurs if you sent out a claim that did not have a diagnosis code entered for the patient. Most insurance companies require at least one diagnosis code on the insurance claim.
You an add diagnosis codes to your patient from the edit client form. For detailed instructions, please see: https://therabill.zendesk.com/entries/22030138-adding-diagnosis-codes-for-a-patient
From the error page: You can get to the edit client form directly from the claim error page in Therabill by clicking the edit icon next to the client name on the right hand side of the page. After you have added the diagnosis code and saved the changes, you can then click the Resubmit Electronically button at the top of the claim error page in Therabill.