I created a new Splunk Cloud trial account today to evaluate it for my team.
After a lot of playing around it appears that I cannot use the trial instance from my code because the host has a self-signed certificate and I cannot find a way to disable the check. I also can't disable HTTPS for the service.
When attempting to publish data to the Splunk HTTP server I get the following exception (every time): "The request was aborted: Could not create SSL/TLS secure channel."
For the full Cloud service (not the trial), you definitely have to work with the Splunk Cloud team to enable SDK access.
I believe that you cannot use the SDK to talk to Splunk in the Cloud Trial version. In the FAQ it says "You can use the REST API, HEC, and SDKs if you have a paid subscription to Splunk Cloud."
Sorry - I should have been clearer, I am using the CSharp HEC to send data to the splunk service. It appears that there is an issue with the certificates that is preventing me from actually sending data. From cURL it works fine.