// Create a customer
const resp = await fetch("https://api.hyfin.app/api/v4/site/YOUR_SITE_ID/customer/addUpdate", {
  method: "POST",
  headers: {
    "Authorization": "Bearer YOUR_API_KEY",
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    displayName: "ABC Plumbing",
    primaryContact: { firstName: "John", lastName: "Doe" }
  })
});

const { success, _id } = await resp.json();