const response = await fetch(
  "http://localhost:3000/api/v1/messages",
  {
    method: "POST",
    headers: {
      "Authorization": "Bearer " + process.env.WA_API_KEY,
      "Content-Type": "application/json"
    },
    body: JSON.stringify({
      session_id: "YOUR_SESSION_ID",
      to: "923001234567",
      body: "Hello from my application!"
    })
  }
);

const result = await response.json();
if (!response.ok) throw new Error(result.error);

console.log(result);