https://apeople.automationanywhere.com/s/article/AWS-secrets-manager-for-CR-user-autologin - Followed the same steps here, I can see from AWS Cloudtrail logs AA is making API call but unable to fetch the key/pair values for the mapped secrets, fails with below error during task execution - 

Could not obtain Username

Found the solution.. their is a small typo in the document causing this issue--

While creating Username and Password as key value pair.. Make it small case like “username” and “password”