BYOC Edge Gateway Stuck on Provisioning State

The stack isn’t deploying past the AWS::EC2::VPC resource, doing jack all to help the provisioning. Admin UI keeps throwing a 422 Unprocessable Entity on the data center mapping even though the EventBridge webhook is routing payloads to the correct Lambda function.

Resources:
 EdgeGateway:
 Type: AWS::ElasticLoadBalancingV2::LoadBalancer
 Properties:
 SubnetMappings:

The architect flow validation is failing on the tenant ID anyway because the VPC peering isn’t matching the expected subnet.