Symfony custom Validator constraint: Not executed (or called?) - php

Question

Hello Stackers,
After readling a lot of documentation, SymfonyCasts and other questions here I still didn't find a cause to my problem. In my opinion, and I could of course be very wrong since the product is so big, I followed the steps as given by the Symfony Docs I still cannot seem to get a Custom Validator Constraint working.
We have a form controller, which I hereby call BasicFormController.php. This is where the actual form submission is sent at. At the end I added an empty response, just to see if it can continue. The problem here is with the the EmailNotFiltered constraint. It get's called here, but after that it just stops.
$constraint = new Assert\Collection([
'firstName' => new Assert\Length(['min' => 1, 'max' => 50]),
'lastName' => new Assert\Length(['min' => 1, 'max' => 50]),
'email' => new ProductAssert\EmailNotFiltered(),
'textWhy' => new Assert\Length(['min' => 20, 'max' => 1000]),
]);
# Validate for all violations.
$violations = $validatorInterface->validate($request->get('data'), $constraint);
# Form contains violations
if (count($violations) >= 1) {
return new JsonResponse(['data' => $violations, 'status' => "error"]);
}
return new JsonResponse([]);
Then the Validator Constraint itself. EmailNotFiltered.php. Nothing weird, just as in the instructions.
namespace App\Validator;
use Symfony\Component\Validator\Constraint;
#[\Attribute]
class EmailNotFiltered extends Constraint
{
public $message = "Invalid email address. Declined by filter.";
public function __construct(array $groups = null, mixed $payload = null)
{
parent::__construct([], $groups, $payload);
}
public function validatedBy()
{
return static::class.'Validator';
}
}
Followed with the Validator, in the same Folder, EmailNotFilteredValidator.php. I've just removed all my own logic to test if I can even get a violation to build.
namespace App\Validator;
use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;
use Symfony\Component\Validator\Exception\UnexpectedTypeException;
use Symfony\Component\Validator\Exception\UnexpectedValueException;
#[\Attribute]
class EmailNotFilteredValidator extends ConstraintValidator
{
public function validate($value, Constraint $constraint): void{
$this->context->buildViolation($constraint->message)
->setParameter('{{ string }}', $value)
->addViolation();
}
}
However, if I throw an exception there, it's not seen. The last place an exception can be thrown and where it will be seen is at the Constraint base file, in the constructor. After that it's done.
I removed all the default logic from the Validator too, just to be sure. But with that, it does not work too. It doesn't really matter, it just doesn't seem to even build up a single violation.
Am I understanding the step-by-step documentation wrong? Or what is the thing I'm doing wrong here?