how do i use brevo api to send whatsapp messages?

following these docs https://mukulsib.readme.io/reference/sendwhatsappmessage

i wrote this code:

import axios from 'axios';

const API_KEY = '/i got api key from brevo SMTP & API page/';

export default async function handler(req, res) {
  if (req.method === 'POST') {
    const { phoneNumbers, Message } = req.body;

    for (const phone of phoneNumbers) {
        const options = {
            method: 'POST',
            headers: {
              accept: 'application/json',
              'content-type': 'application/json',
              'api-key': API_KEY,
            },
            body: JSON.stringify({
                senderNumber: '123456789', 
                text: Message, 
                contactNumbers: [phone,]
            })
        };

            try {
                const response = await axios.request(options);
                console.log(`Message sent successfully to ${phone}`);
                console.log('Response data:', response.data);
            } catch (error) {
                console.error(`Error sending message to ${phone}:`, error.message);
            }
        }
    
            res.status(200).json({ message: 'Messages sent' });
        } else {
            res.status(405).json({ error: 'Method not allowed' });
        }
    }

and when i try it on the docs page i get this error:
{“code”: “permission_denied”, “message”: “Your account is not registered”}