To enable fast iteration and consistent deployment, you can use AWS Cloud Development Kit (AWS CDK) version 2, AWS CloudFormation, and Terraform. The recommended services are built with observability in mind, with process level metrics, logs, and dashboards. Extend these mechanisms to meet your needs and create alarms in Amazon CloudWatch to notify your on-call team of any issues.

The payment backend is protected with API Gateway resource policies to allow your API to be securely invoked from known resources. When you choose managed services, you can be sure that all AWS API calls are done through HTTPS endpoints using TLS communication, which will protect your data in transit.

All components scale automatically, and the account limits should be clearly defined for the supported product range to avoid affecting reliability. To further increase reliability, consider implementing a disaster recovery plan for your solution by initiating cross-region failover using Route 53 for the whole infrastructure. 

Managed serverless solutions can help you avoid having to worry about scaling requirements. Fargate removes the need to own, run, and manage a compute infrastructure, allowing you to focus on payment processing. Network Load Balancer distributes incoming traffic across multiple targets, which can handle millions of requests per second.

This Guidance is designed to help you build a serverless architecture that keeps costs down. You pay only for the time and resources used to process payments. With managed and serverless services, you can set attributes that ensure sufficient capacity. You must set and monitor these attributes so that you minimize excess capacity and maximize performance. 

To reduce the amount of hardware required for provisioning, consider using managed container services, such as Fargate, instead of implementing your own container infrastructure.