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.
I think it is poor form to make a comment asking for help in a negative way and then delete it (as the email thread from this gist shows). Please stand behind your words. I would like to work this out, but when you do things like that, I get the feeling you want it all "your way". Since you are the developer of FeedLand, only you can see what is happening in the app beyond the Javascript console. I have supplied a lot of data showing my investigation of the problems with the WordPress rssCloud implementation, but I can only investigate things from "the outside" for the most part.