jQuery validate does not work in modal

Question

I have a modal with a form. I used this plugin to create the modal: https://github.com/samdark/the-modal

I also use jquery validate.

It works on all forms of my site. However in the form that is within my modal it does not work.

Does anyone have any idea?

HTML:

        <form id="form-contato" action="enviar.php" method="post">

            <h5>Deixe sua mensagem</h5>

            <input type="hidden" name="field-home">

            <div>
                <label>Nome <span>*</span></label><br>
                <input type="text" name="nome_completo" class="input-full" required="true">
            </div>

            <div>
                <label>E-mail <span>*</span></label><br>
                <input type="email" name="email" class="input-full" required="true">
            </div>

            <div>
                <label>Telefone</label><br>
                <input type="text" name="telefone" class="input-half">
            </div>

            <div>
                <label>Assunto </label><br>
                <input type="text" name="assunto" class="input-full">
            </div>

            <div>
                <label>Mensagem <span>*</span></label>
                <textarea name="mensagem" class="input-textarea" required="true"></textarea>
            </div>

            <button type="submit" class="enviar">
                Enviar <i class="fa fa-paper-plane" aria-hidden="true" style="margin-left: 5px;"></i>
            </button>

<script>
$("#form-contato").validate({
            rules : {
                nome_completo: {
                    required:true
                },
                email: {
                    required:true,
                    email:true
                },
                mensagem: {
                    required:true
                }
            },
            messages:{
                nome_completo: {
                    required: "Campo obrigatório."
                },
                email:{
                    required: "Campo obrigatório.",
                    email: "Informe um e-mail válido."
                },
                mensagem: {
                    required: "Campo obrigatório."
                }
            }
        });
</script>