I have a test application running at test.rsscloud.io on ports 80 and 9876.
The following code works:
curl --location --request POST 'https://brokenriverbooks.com/?rsscloud=notify' \
--header 'Content-Type: application/x-www-form-urlencoded' \
--data-urlencode 'domain=test.rsscloud.io' \
--data-urlencode 'port=80' \
--data-urlencode 'path=/feedupdated-s8759' \
--data-urlencode 'registerProcedure=' \
--data-urlencode 'protocol=http-post' \
--data-urlencode 'url1=https://brokenriverbooks.com/feed/'
However if you change the port to 9876 it fails. For some reason the rssCloud plugin seems unable to hit ports that are not 80.
Andrew, I just did a test with my WordPress.com blog (https://rsscloud4.wordpress.com/feed/), and it took 60 minutes for the post to appear on FeedLand. Could you perform another test with your feed (https://andrewshell.wordpress.com/feed/)? I will do some additional tests with my WordPress.com blog and my WordPress.org blog with the RSS Cloud plugin. Based on my test, it seems that FeedLand is still having problems with RSS Cloud for WordPress.com blogs.