For IPv4 traffic, private subnets require a NAT gateway in a public subnet to access the internet. NAT gateways must be deployed in public subnets and associated with an Elastic IP address. Private subnet route tables must direct 0.0.0.0/0 traffic to the NAT gateway.

The question states that NAT gateways are incorrectly placed in private subnets, which cannot provide internet access. Deploying NAT gateways in public subnets resolves this issue and restores outbound connectivity to external APIs.

Option A applies only to IPv6. Option B adds unnecessary complexity. Option D is not applicable because external APIs are not AWS services.