Certificates can be a pain.
So if you're trying to use UTL_HTTP or APEX_WEB_SERVICE to reach https destinations you'll be on the hook for obtaining certificates for the target server.
I had access to all the certificates separately and loaded them into a nice fresh new wallet. Unfortunately I couldn't get this to work. I'm working an SR with Oracle now but there doesn't seem to be much expertise on troubleshooting issues, even with