Some feeds may return an error when you try to parse (or subscripe to them) via RSS API. This could be the case when the webserver hosting the feed is blocking automated traffic. If you have control over the target server, you may whitelist our IP-Addresses to ensure that RSS API can access all of your feeds. You can find an up-to-date list of our IP-Space here. Please contact us for further help/troubleshooting.