Following "Adding Custom HL7 FHIR packages to the HL7 FHIR server" at https://learning.intersystems.com/course/view.php?id=1721 I'm able to create an FHIR extension of type string as well as a search parameter.

However, I need to create an extension as well as a search parameter of type Reference. And this is not working.

Did anyone successfully add an extension and search parameter of type Reference?