html formumda submit butonuna/enter'a basınca hata mesajı veriyor

<form action="index.php" method="POST" class="u-clearfix u-form-spacing-10 u-form-vertical u-inner-form" style="padding: 10px;">
                <div class="u-form-group u-form-name">
                  <label for="name-e3bb" class="u-label">E-Posta</label>
                  <input type="text" id="name-e3bb" name="email" value="<?php echo $_SESSION["email"] ?>" class="u-border-1 u-border-white u-input u-input-rectangle u-radius-5 u-input-1" required="">
                </div>
                <div class="u-form-group u-form-group-2">
                  <label for="text-9cb9" class="u-label">Discord:</label>
                  <input type="text" placeholder="" id="text-9cb9" name="discord" value="<?php echo $_SESSION["discord"] ?>" required="" class="u-border-1 u-border-white u-input u-input-rectangle u-radius-5 u-input-2">
                </div>
                <div class="u-form-email u-form-group">
                  <label for="email-e3bb" class="u-label">Yeni Şifre:</label>
                  <input type="password" id="email-e3bb" minlength="8" name="password" class="u-border-1 u-border-white u-input u-input-rectangle u-radius-5 u-input-3" required="" autofocus="autofocus">
                </div>
                <div class="u-form-group u-form-group-4">
                  <label for="text-3db2" class="u-label">Yeni Şifre Tekrar:</label>
                  <input type="password" placeholder="" minlength="8" id="text-3db2" name="repassword" class="u-border-1 u-border-white u-input u-input-rectangle u-radius-5 u-input-4" required="">
                </div>
                <div class="u-align-right u-form-group u-form-submit">
                  <button name="kaydet" value="submit" class="u-border-none u-btn u-btn-submit u-button-style u-custom-color-2 u-hover-custom-color-4 u-btn-1">Güncelle</button>
                  <input type="submit" name="kaydet" value="submit" class="u-form-control-hidden">
                </div>
              </form>