public function followChannel($userIdentifier, $channelIdentifier, $accessToken, $notifications = false)
    {
        if ($this->apiVersionIsGreaterThanV3()) {
            if (!is_numeric($userIdentifier)) {
                throw new InvalidIdentifierException('user');
            }

            if (!is_numeric($channelIdentifier)) {
                throw new InvalidIdentifierException('channel');
            }
        }

        if (!is_bool($notifications)) {
            throw new InvalidTypeException('Notifications', 'boolean', gettype($notifications));
        }

        return $this->put(
            sprintf('users/%s/follows/channels/%s', $userIdentifier, $channelIdentifier),
            ['notifications' => $notifications],
            $accessToken
        );
    }