g-recaptcha-Response returns no value

Question

The registration form sends the data by ajax, the captcha is completed correctly, and the token is given also as I could verify by the command. However when submitting the form I see that the value is empty.

Ajax code

var dados = new FormData(this);
            jQuery.ajax({           //Função AJAX
        url:"login-system/registrar.php",           //Arquivo php
        type:"post",                //Método de envio
        data: dados,    //Dados
        dataType: 'json',
        processData: false,
        cache: false,
        contentType: false,
        beforeSend: function(){ jQuery("#registrar").html('Criando Cadastro...');},
        success: function (result){         //Sucesso no AJAX
        jQuery("#registrar").html('Registrar');

Form

<form action="#" id="form" method="post">
             <input type="hidden" name="csrf_token" value="<?php echo $secure->reg_token(); ?>" />
             <label id="status" style="display:none;color:red;"></label>
                    <div class="form-group">
                        <label>Usuário</label>
                        <div class="input-group">
                        <div class="input-group-addon"><i class="fa fa-user"></i></div>
                        <input type="text" id="usuario" name="usuario" onkeyup="mascara( this, alphanum )" onkeypress="document.getElementById('errouser').innerHTML = '';" maxlength="8" class="form-control" placeholder="Usuário (Utilizado para Login)" autocomplete="off">
                        </div>
                        <span class="help-block" id="errouser"></span>
                    </div>
                    <div class="form-group">
                        <label>Senha</label>
                        <div class="input-group">
                        <div class="input-group-addon"><i class="fa fa-asterisk"></i></div>
                        <input type="password" id="senha" name="senha" onkeyup="validatepass(this);" maxlength="12" class="form-control" placeholder="Senha (Utilizado para Login)" autocomplete="off">
                        </div>
                        <span class="help-block" id="erropass"></span>
                    </div>
                    <div class="form-group">
                        <label>Repita a Senha</label>
                        <div class="input-group">
                        <div class="input-group-addon"><i class="ti ti-back-right"></i></div>
                        <input type="password" id="repsenha" name="repitasenha" onkeyup="validaterep(this);" maxlength="12" class="form-control" placeholder="Repita a Senha" autocomplete="off">
                        </div>
                        <span class="help-block" id="errorepsenha"></span>
                    </div><div class="form-group">
                        <label>E-mail</label>
                        <div class="input-group">
                        <div class="input-group-addon"><i class="ti ti-email"></i></div>
                        <input type="email" id="email" name="email" onkeyup="document.getElementById('erroemail').innerHTML = '';" maxlength="30" class="form-control" placeholder="E-mail de Segurança (Recuperação de Senha)" autocomplete="off">

 <label>Verificação de Segurança</label>
                    <div class="g-recaptcha" data-sitekey="6Lev8WUUAAAAADY1OAgqFezg4Jb-TAUiv5s3Y0el" data-callback="recaptcha"></div>
                    <span class="help-block" id="errocaptcha"></span>
                     </div>         
                    <button type="submit" id="registrar" class="btn btn-success btn-flat m-b-30 m-t-30">Registrar-se</button>
                    <div class="register-link m-t-15 text-center">
                        <p>Possui conta? <a href="login.php"> Logue-se!</a></p>
                    </div>
                </form>