Entenda a integração antes do código.

curl --request POST "https://app.connect.mydev.com.br/api/v1/instances/INSTANCE_ID/messages" \
  --header "Authorization: Bearer $CONNECT_TOKEN" \
  --header "Accept: application/json" \
  --header "Content-Type: application/json" \
  --data '{"to":"DESTINATARIO","text":"Olá!"}'

const response = await fetch(
  `https://app.connect.mydev.com.br/api/v1/instances/${process.env.CONNECT_INSTANCE_ID}/messages`,
  {
    method: 'POST',
    headers: {
      Authorization: `Bearer ${process.env.CONNECT_TOKEN}`,
      Accept: 'application/json',
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({ to: process.env.CONNECT_TO, text: 'Olá!' }),
  },
);
if (!response.ok) throw new Error(`Connect: HTTP ${response.status}`);
const result = await response.json();

$instance = rawurlencode(getenv('CONNECT_INSTANCE_ID'));
$ch = curl_init("https://app.connect.mydev.com.br/api/v1/instances/$instance/messages");
curl_setopt_array($ch, [
    CURLOPT_POST => true,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_TIMEOUT => 20,
    CURLOPT_HTTPHEADER => [
        'Authorization: Bearer '.getenv('CONNECT_TOKEN'),
        'Accept: application/json',
        'Content-Type: application/json',
    ],
    CURLOPT_POSTFIELDS => json_encode(['to' => getenv('CONNECT_TO'), 'text' => 'Olá!']),
]);
$body = curl_exec($ch);
$status = curl_getinfo($ch, CURLINFO_HTTP_CODE);
if ($body === false || $status >= 400) throw new RuntimeException('Falha ao enviar pelo Connect');
$result = json_decode($body, true, 512, JSON_THROW_ON_ERROR);