Add following validation code under contact controller store () method.
$this->validate($request, [
'first_name' => 'required',
'last_name' => 'required',
'email' => 'required',
'city' => 'required',
'country' => 'required',
'feedback' => 'required',
]);
After that, in the view show if any errors
@if($errors->any())
<div class="alert alert-danger">
@foreach($errors->all() as $error)
<p>{{ $error }}</p>
@endforeach
</div>
@endif
For more about controller validation - https://grails.com/docs/5.0/validation#controller-validation