An S3 gateway endpoint is configured in a VPC whose private subnets lack outbound internet access. A user on an EC2 instance in one of those private subnets is unable to PUT a file into an S3 bucket in the same Region. Which change will resolve the upload failure?

The S3 gateway endpoint allows instances in private subnets to access S3 without traversing the public internet. However, for the endpoint to be effective, the subnet's route table must explicitly include routes for S3. The correct solution is to add the S3 prefix-list routes (which represent S3's IP ranges) to the subnet's route table, directing traffic for S3 to the S3 gateway endpoint. Adding s3:PutObject permissions is necessary but doesn't resolve the network connectivity issue. Modifying the security group for outbound traffic on port 80 is incorrect because S3 uses HTTPS (port 443), and even then, direct internet access is not the goal when using a gateway endpoint. Altering the S3 bucket policy might be needed for cross-account access or specific controls, but it won't fix a routing problem within the VPC.