Symptom
Account A created an S3 bucket and configured access permissions so that Account B’s DMS (Database Migration Service) instance can upload files to Account A’s S3 bucket.
The file list uploaded by Account B’s DMS is visible in Account A’s S3. However, when attempting to download those files, the following error occurs, making download and file usage impossible.
Solution
If resources belong to the same AWS account, you can grant users access to specific bucket folders. However, since two different accounts are involved here, cross-account access must be used.
Create an IAM role or user in Account A that applies to Account B, and then grant GetObject and PutObject permissions in the corresponding IAM policy.