Cannot execute private API gateway endpoint in VPC A from an application loadbalancer in VPC B although VPC Peering is done

Hi

Please refer this link for the reference https://repost.aws/knowledge-center/invoke-private-api-gateway

Check this points:

Security Group Rules:

• Double-check the security groups involved. Ensure the ALB's security group in VPC B has inbound rules that allow traffic on the appropriate port (typically HTTPS - port 443) from the CIDR block of the subnets where the API Gateway endpoint resides in VPC A.
• Verify the security group for the API Gateway endpoint in VPC A has outbound rules that allow traffic on the same port (443) to the CIDR block of the subnets where the ALB resides in VPC B.

VPC Endpoint Configuration:

Ensure an interface VPC endpoint is created in VPC B for API Gateway service (directs traffic within VPC)

*Additional References: *

How to invoke a private API - Amazon API Gateway: https://docs.aws.amazon.com/apigateway/latest/developerguide/apigateway-private-api-test-invoke-url.html

Deploy an Amazon API Gateway API on an internal website using private endpoints and an Application Load Balancer: https://docs.aws.amazon.com/prescriptive-guidance/latest/patterns/deploy-an-amazon-api-gateway-api-on-an-internal-website-using-private-endpoints-and-an-application-load-balancer.html