A development team has set up a new IAM user and granted it the s3:putObject permission, allowing it to write objects to an S3 bucket. This particular S3 bucket employs server-side encryption using AWS KMS managed keys (SSE-KMS) as its default encryption method. However, when the application attempts to use the access key ID and secret access key of the IAM user to call the PutObject API, it encounters an access denied error.

As a Developer Associate, what steps would you take to resolve this issue?