Filter\FilterFailedException is thrown when a validation filter fails and FILTER_THROW_ON_FAILURE is set.

<?php

try {
    $email = filter_var(
        'not an email',
        FILTER_VALIDATE_EMAIL,
        FILTER_THROW_ON_FAILURE
    );
} catch (Filter\FilterFailedException $e) {
    echo "The value did not pass validation.\n";
}

This exception represents validation failure, not an unknown filter. If the filter ID itself comes from a name or configuration, check it separately before calling filter_var():

<?php

$filter = filter_id('validate_email');

if ($filter === false) {
    throw new InvalidArgumentException('Unknown filter.');
}

try {
    $email = filter_var(
        'not an email',
        $filter,
        FILTER_THROW_ON_FAILURE
    );
} catch (Filter\FilterFailedException $e) {
    echo "The value did not pass validation.\n";
}