In order for RPC over HTTP to work you must have a Trusted CA Root Certificate installed and configured. This video describes a situation where you are using a self-signed certificate you will need to install the certificate into the Trusted Root Certification Authorities store.
How to find in which host the Repository Integration service is running in a multi node domain
How to unassign services from an expired key and assign them to a valid key in 9.1.0 and 9.5.1
Converting and adding of a self signed certificate to use a Webservice Consumer transformation