[FOSRestBundle] Showing custom Exception message no working fix

 If ./config/packages/fos_rest.yaml:

fos_rest:

    exception:

        messages:

            Symfony\Component\HttpKernel\Exception\HttpException: true

for you too, you can inject this service manually like this in services.yaml:

fos_rest.exception.messages_map:

        class: FOS\RestBundle\Util\ExceptionValueMap

        public: false

        arguments:

            - { Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException: true }

thanks to https://github.com/FriendsOfSymfony/FOSRestBundle/issues/1522