Other frameworks

createInverseHandler returns a function from a Fetch API Request to a Response, so it runs wherever that API exists.

// Remix / React Router
export const action = ({ request }: ActionFunctionArgs) => inverse(request);

// Hono
app.post("/api/inverse", (c) => inverse(c.req.raw));

// SvelteKit: src/routes/api/inverse/+server.ts
export const POST = ({ request }) => inverse(request);

// Astro: src/pages/api/inverse.ts
export const POST: APIRoute = ({ request }) => inverse(request);

For Express or Fastify, call handleDeclaration(body, options) directly. It takes the parsed body and returns the same result object:

app.post("/api/inverse", express.json(), async (req, res) => {
  const result = await handleDeclaration(req.body, options);
  res.status(result.ok ? 200 : result.error === "invalid" ? 422 : 400).json(result);
});

Without JavaScript

The handler also accepts application/x-www-form-urlencoded, so a server-rendered form works. Send kind, the fields and, for items, repeat items. You are responsible for the review step: render the entered data with declarationFields() and a submit button labelled with getMessages(locale).withdrawal.confirm.

Request body

{
  "kind": "withdrawal",
  "locale": "de",
  "data": { "name": "Erika Muster", "email": "erika@example.com", "contractRef": "A-1001" }
}

Responses: 200 { ok: true, id, kind, receivedAt, copy, endsAt? }, 422 { ok: false, error: "invalid", errors }, 400 for an unknown kind, 405 for other methods, 500 when storing failed.