The payer is telling you that this is a Medicare plan but you submitted with a plan type of Blue Cross/Blue Shield. You need to change the plan type indicator to Medicare Part B on the insurance card that you have set up for this client.
How to Fix
On the right hand side of the EDI error page in Therabill, click the edit icon next to the client name. The edit client form will open up. On the right of the edit client form you will see the list of insurance cards that you have entered for the client. Click the edit icon associated with the insurance card that you submitted to and received this error from. The edit insurance card form will open up. Under the Policy Info sections of the edit insurance card, change the Plan Type to Medicare Part B and then click the Apply Edits button at the bottom of the form.
VERY IMPORTANT: Click the Save button at the bottom of the edit client form.
Now that you have changed the plan type, you can now click the Resubmit Electronically button at the top of the EDI error page for this error in Therabill.