$stmt = $conn->prepare("INSERT INTO survey_responses (token, respondent_area, question_code, response) VALUES (?, ?, ?, ?)");

foreach ($_POST['respostas'] as $area => $questions) {
    foreach ($questions as $question_code => $response) {
        $stmt->bind_param("sssi", $token, $area, $question_code, $response);
        $stmt->execute();
    }
}