Preview

Run the model's pure decide and report what a command would produce: the events, the state after them, and the proration it would charge.

Source: packages/paykit/src/Billing/Preview.binding.ts Kind: Binding · Product: Subscription · Provides: Paykit.Preview

Run the model’s pure decide and report what a command would produce: the events, the state after them, and the proration it would charge. Nothing is recorded, and the answer cannot disagree with the write it previews because it is the same function.

A model refusal comes back as _tag: "rejected" — data, not a failure — so a console or an agent can show why before anyone sends anything.

Showing the charge first

const preview = yield* Paykit.Preview(account);
const answer = yield* preview({ command: { kind: "changeTier", tier: "scale" } });
if (answer._tag === "accepted" && answer.proration !== undefined) show(answer.proration.due);