Your e-commerce company is shifting its software development approach from the traditional waterfall methodology to a more efficient continuous integration and continuous deployment (CI/CD) pipeline. Every application is now required to adhere to best CI/CD practices, be packaged as Docker containers, and subsequently deployed. These Docker images are to be stored in the Amazon Elastic Container Registry (ECR) and pushed using AWS CodePipeline and AWS CodeBuild.

During the implementation, the final step fails due to an authorization issue. What is the most probable cause of this failure?