The above answers maybe valid for the relevant case. One case, in which you get "AWS CodeCommit - fatal: repository 'https://git-codecommit...' not found" is, when the IAM user doesn't really exist (who want to clone the repo) for the specific AWS account. Let's say the user has access to AWS CodeCommit on one AWS account but he is trying to clone a repo from another (different) AWS account. So double check if the IAM user exist on the target AWS account.