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.


Also if that is the problem they surely could provide a better error message. I thought from the message they returned that it was a syntax error of some kind.