aws iot describe-endpoint
An error occurred (AccessDeniedException) when calling the DescribeEndpoint operation: User: arn:aws:iam::548217278864:user/name is not authorized to perform: iot:DescribeEndpoint because no identity-based policy allows the iot:DescribeEndpoint action
This the common problem most new-comers will face. First create your Policy and attach it to your Certificate. If still also same error continues, then it means you have not assigned it the User. For this go to IAM and create the your Policy (usually go with same name as in iot-core) and select that Policy and assign it to the respective User.