After installing on a search head I have filesystem-access to, I was pleased to discover I could configure xMatters credentials in Splunk's /manager UI and proceed to test & verify Saved Search -> Alert Action -> call xMatters -> receive Notifications.
After SplunkCloud Ops installed the same version in a maintenance window (SH requires restart), the link was not visible in the SplunkCloud /manager.
copied the URL from a non-prod, non-SplunkCloud instance and I was able to access the configuration properties for the splunkbase.splunk.com/app/2901/ App, xMatters Actionable Alerts for Splunk
...didn't need the absent link in /manager afterall.
@nmclaughl1 If your problem is resolved, please accept an answer to help future readers.
In your dev/test instance, your configurations appear in $SPLUNK_HOME/etc/apps//local
You can create a custom app with local folder having similar config but with production details and ask splunk support to deploy it. It should work. [ you can test the same in in your dev, by creating the custom app having contents/configs of local folder].
I assume you have followed https://help.xmatters.com/integrations/logmgmt/splunk.htm?cshid=Splunk