A medical bill denial happens when your insurer refuses to pay for a service, procedure, or treatment — often shown on your Explanation of Benefits (EOB) with codes like CO-50, CO-197, CO-B7, or PR-2. The good news: many denials are appealable, but deadlines can be as short as 60 to 180 days. Use our free Medical Bill Denial Appeal Builder below to generate a regulation-cited appeal letter and tracking sheet in minutes.