Medicare Error: Referral Attached, but Receiving No Referral Error

What does this error mean?

If the referral is selected on the invoice, it is likely the error is being caused by a setting in Preferences called Include Referral for Medicare Billing.

How do I resolve this error?

Open the provider's Preferences > Invoices tab, and ensure that Include Referral for Medicare Billing is set to Yes, and click Save if you made any changes.