Plug it into what you already run.
The plugins are free, unencoded and carry no licence check. The API key is the only thing that connects a shop to an account.
CubeCart 6.8
Captures the referral on landing, holds it server side against the session, ties it to the order as the order is created, and reports when the order reaches a status you choose. Line items, quantities and the coupon used are all sent, so commission can be set per product. Includes a local queue, retry, and an admin screen showing recent events, errors and a connection test.
WooCommerce
Order status drives the conversion and a refund drives the clawback. The proportion is calculated at send time, so a part refund claws back the matching part of the commission.
WHMCS 8
Runs alongside the built-in affiliate system. It distinguishes a renewal from a first payment, so a subscription earns recurring commission against the original referral instead of being counted as a new sale.
Stripe
For subscription businesses with no shopping cart. First payment, renewal and credit are each reported as their own event kind, with the referral held on the subscription so it survives for the life of the customer.
PHP SDK
One file and no Composer dependency, so it drops into an application with no package manager. It is the same client the plugins use.
REST API and webhooks
Everything the console can do. Scoped keys, test and live modes, idempotency on every write, dated versioning, and signed outbound webhooks with a published retry ladder and a replay button.