Commerce reference implementation samples as integration templates
Key Takeaway
Use a reference sample as a template: adapt it to your gateway or service, then map it to your store in StoreIntegratedService.
Commerce reference implementations are sample packages and code, hosted on GitHub, that show how to connect a store's checkout and payments to outside services. You use them as templates, so you start from a sample and adapt it to your own gateway or service. You then register your Apex classes and map them to your store.
The reference samples on GitHub
The reference payments integration package supports B2B Commerce implementations. You can use it as a template to create your own payments package. You clone or download the package from GitHub. The package is available in Enterprise, Unlimited, and Developer Editions.
A separate GitHub repository, the CommercePayments Gateway Reference Implementation for Payeezy, holds sample code for a Payeezy payment gateway built with the CommercePayments namespace. Review that code when you need help configuring your own payment gateway implementation.