...
Please see the "rest" section of the corresponding CapabilityStatement for details of which endpoints are supported:
http://fhir.patientsknowbest.com/capabilitystatement/aggregatoraggregated
Note: the above CapabilityStatement reflects which resource types are included in the aggregation logic, and therefore available from the Aggregated FHIR endpoint. Searches over other resource types will return an empty search result; you should not assume a “successful” response implies the corresponding resource type has been added to the aggregation logic.
...