OK, I have changed from https to http. Now I receive this error:
[12-10-2017 04:05:28] [Error] WPRSS > wprss_get_feed_items:
Failed to fetch feed “http://news.kitco.com/rss/”. A feed could not be found at http://news.kitco.com/rss/. A feed with an invalid mime type may fall victim to this error, or SimplePie was unable to auto-discover it.. Use force_feed() if you are certain this URL is a real feed.
[12-10-2017 04:05:28] [Error] WPRSS > 2:
Sorted:
When I validate the feed, it says
Congratulations!
[Valid RSS] This is a valid RSS feed.
Recommendations
This feed is valid, but interoperability with the widest range of feed readers could be improved by implementing the following recommendations.
Feeds should not be served with the “text/xml,text/xml” media type [help]
line 1749, column 2: Missing atom:link with rel=”self” [help]
</channel>
