Why is the form validator not working?

Question

symfony

public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('postcode', IntegerType::class, [
                'required' => true,
                'attr' => [
                    "min" => "1000",
                    "max" => "99999",
                    'minMessage' => 'min error message'
                    , 'maxMessage' => 'max error message'
                ],
                'constraints' => array(
                    new Constraints\NotBlank(),
                    new Constraints\Type('integer'),
                    new Constraints\Regex(array(
                            'pattern' => '/^[0-9]\d*$/',
                            'message' => 'Please use only positive numbers.'
                        )
                    ),
                    new Constraints\Length(array('min' => 4, 'max' => 5))
                )
            ]);
 }

after submitting an empty field, it gives a message that the field cannot be empty, and when filled with numbers like 12, 123, 1234567,
the form is valid and there are no messages