In this tutorial, we are going to see how to solve the error CCAvenue Error Code 21011 billing email . This error occurs while connecting an application to the CCAvenue payment gateway . It is really a very small mistake sometimes made by a developer but later becomes a headache to solve this issue. Reason of error CCAvenue Error Code 21011 billing email This error is a result of missing some value that is needed while integration of the code in the application. Value is related to an input that is needed in the form integrated in an application. In the guidelines of integration provided by CCAvenue that are necessarily needed to be followed while integrating it into the application. Some Input values are required means must have values like amount , currency , merchant_id , redirect_url , cancel_url etc are minimum required and should be included in the form before sending the data to the CCAvenue page. If we avoid them or forget to use them in the code, CCAvenue throws an e