Customer portal

const response = await fetch("https://merchant.zahlo.eu/api/v1/customer-portal/sessions", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "x-api-key": process.env.ZAHLO_API_KEY,
    "Idempotency-Key": `portal-${customer.id}-${requestId}`,
  },
  body: JSON.stringify({
    customerId: customer.id,
    returnUrl: "https://app.example.com/settings/billing",
  }),
});
if (!response.ok) throw new Error(`portal session failed: ${response.status}`);
const { url } = await response.json();
// Return url to the browser; do not proxy the API key.