I'm trying to get a modal window to confirm whether or not you want to register a user, I'm using php to make it add, the modal window comes out but when you click on the save button, it does not do anything , here I leave the code
This is the code of my form
<div class="container-fluid">
<div class="row">
<div class="col-md-12">
<div class="card col-md-6">
<div class="card-body">
<div class="panel panel-default">
<div class="panel-body">
<form method="post" id="f" action="add_user.php">
<div class="col-md-12">
<div class="input-group mb-3">
<div class="input-group-prepend">
<span class="btn btn-info">Cedula</span>
</div>
<input type="text" class="form-control" id="cedula" name="cedula" placeholder="Cedula" required onkeypress="return valida(event)" minlength="7">
<div id="Info"></div>
</div><!-- ./form-group -->
<div class="input-group mb-3">
<div class="input-group-prepend">
<span class="btn btn-info">Nombre</span>
</div>
<input type="text" class="form-control" id ="full-name" name="full-name" placeholder="Nombre completo" required onkeypress="return letras(event)">
</div><!-- ./form-group -->
<div class="input-group mb-3">
<div class="input-group-prepend">
<span class="btn btn-info">Usuario</span>
</div>
<input type="text" class="form-control" id="username" name="username" placeholder="Nombre de usuario" required>
<div id="nfo"></div>
</div><!-- ./form-group -->
<div class="input-group mb-3">
<div class="input-group-prepend">
<span class="btn btn-info">Contraseña</span>
</div>
<input type="password" class="form-control" id="password" name ="password" placeholder="Contraseña" required minlength="8">
</div><!-- ./form-group -->
<div class="input-group mb-3">
<div class="input-group-prepend">
<span class="btn btn-info">Rol de Usuario</span>
</div>
<select class="form-control" id="level" name="level" required>
<option value="">Selecciona el tipo de usuario</option>
<?php foreach ($groups as $group ):?>
<option value="<?php echo $group['group_level'];?>"><?php echo ucwords($group['group_name']);?></option>
<?php endforeach;?>
</select>
</div><!-- ./form-group -->
<div class="input-group mb-3">
<div class="input-group-prepend">
<span class="btn btn-info">Status Usuario</span>
</div>
<select class="form-control" id="status" name="status" required>
<option value="">Selecciona el status del usuario</option>
<option value="1">Activo</option>
<option value="0">Inactivo</option>
</select>
</div><!-- ./form-group -->
<div class="form-group clearfix" style="float: right;">
<button type="submit" id="ad" name="add_user" class="btn btn-primary" data-toggle="modal" data-target="#exampleModalCenter" >Crear</button>
</div><!-- ./form-group -->
</div><!-- ./col -->
</form>
</div><!-- ./panel-body -->
</div><!-- ./panel default -->
</div><!-- ./card-body -->
</div><!-- /.card -->
</div><!-- /.col -->
</div><!-- /.row -->
</div><!--/. container-fluid -->
and this is the code of my modal
<div class="modal fade" id="exampleModalCenter" tabindex="-1" role="dialog" aria-labelledby="exampleModalCenterTitle" aria-hidden="true">
<div class="modal-dialog modal-dialog-centered" role="document">
<div class="modal-content">
<div class="modal-header">
<h5 class="modal-title" id="exampleModalLongTitle">¿Esta seguro de crear el usuario?</h5>
<button type="button" class="close" data-dismiss="modal" aria-label="Close">
<span aria-hidden="true">×</span>
</button>
</div>
<div class="modal-body">
Compruebe que los datos son correctos antes de crear el usuario
</div>
<div class="modal-footer">
<button type="button" class="btn btn-primary">Crear Usuario</button>
<button type="button" class="btn btn-secondary" data-dismiss="modal">Cerrar</button>
</div>
</div>
</div>
</div>