Form Submit Button not work on Smartphone

I have an app developed in VueJs. I have a contact form. This form is working perfectly in different browsers, however when trying to use this form on a smartphone or tablet it doesn't work.

And I tried to implement it in two ways but the problem persists. implementation 1:

<form @submit.prevent="send_message">
            <form-group>
              <label for="name" class="required">Nome:</label>
              <input
                type="text"
                name="name"
                id="name"
                class="form-control"
                required
                v-model="msg.name"
                placeholder="Seu nome completo"
              />
            </form-group>

            <form-group>
              <label for="email" class="required">E-mail:</label>
              <input
                type="email"
                name="email"
                id="email"
                class="form-control"
                required
                placeholder="Seu e-mail"
                v-model="msg.email"
              />
            </form-group>

            <form-group>
              <label for="subject" class="required">Assunto :</label>
              <input
                type="text"
                name="subject"
                id="subject"
                class="form-control"
                placeholder="Assunto da Mensagem"
                required
                v-model="msg.subject"
              />
            </form-group>

            <form-group>
              <label for="message" class="required">Mensagem:</label>
              <textarea
                name="message"
                id="message"
                class="form-control"
                placeholder="Conteúdo da Mensagem"
                required
                v-model="msg.message"
              />
            </form-group>

            <p><span class="text-danger">*</span>Campos obrigatórios</p>

            <button class="add btn btn-gradient-primary font-weight-bold todo-list-add-btn ml-0 ml-lg-2 mt-2 mt-lg-0" id="add-task">Add</button>  
          </form>