aws-config.js is used by browser sessions to configure the SDK.aws-exports.js is used by SPA applications that are packed (by Webpack, Browserify, or similar tools) to configure the SDK.
You need the aws-exports.js file for the React app. You can download this file from the Amazon S3 bucket using either the AWS Mobile Hub console or the AWS CLI. To download via the CLI, use the following:
aws s3 cp s3://bucket/aws-exports.js ./src/aws-exports.js