Yunwei Wang: http://build.fhir.org/valueset-operation-expand.html#examples
In this example

POST [base]/ValueSet/23/$expand
[other headers]

{
"resourceType" : "Parameters",
"parameter" : [
{
"name" : "valueSet",
"resource" :

Unknown macro: { "resourceType" }

}
]
}

Since the value set is provided as an input parameter, the URL should NOT have valueset id.

Correction:  POST [base]/ValueSet/$expand{{}}