Confluent DynamoDbSinkConnector on AWS Private VPC

Trying to connect from kafka-connect container running on ec2 linux to DynomoDb, both running on same private VPC. Used the following instructions IAM roles for Amazon EC2 - Amazon Elastic Compute Cloud (replacing s3access with the appropriate role) to get temporary credentials and set AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY env vars for kafka-connect container.

Receive the following in the container logs:

The security token included in the request is invalid

Any guidance is appreciated