Does this only pertain to those that use IRIS as a FHIR Repository?

I was able to figure it out, and get it to work..

Class osuwmc.DataLookup.REST.TableLookup Extends osuwmc.DataLookup.REST.Base
{

Parameter Version = "1.0.0";

Parameter HandleCorsRequests = 0;

XData UrlMap [ XMLNamespace = "http://www.intersystems.com/urlmap" ]
{
<Routes> 
    <!-- Server Info -->
    <Route Url="/" Method="GET" Call="GetInfo" />
    <Route Url="/EpicDepartment" Method="GET" Call="GetAllEpicDepartments" />
    <Route Url="/EpicDepartment/:departmentID" Method="GET" Call="GetEpicDepartment"/>
    </Routes>
}

ClassMethod GetInfo() As %Status
{
    SET version = ..#Version
    SET info = {
      "version": (version)
    }
    RETURN ..%ProcessResult($$$OK, info)
}

ClassMethod GetAllEpicDepartments() As %Status
{
    SET tSC = $$$OK
    set %response.ContentType = ..#CONTENTTYPEJSON
    set rset = ##class(osuwmc.Epic.Clarity.DepartmentMaster).ExtentFunc()
    write "["
    if rset.%Next(){
      set department = ##class(osuwmc.Epic.Clarity.DepartmentMaster).%OpenId(rset.ID1)
      do department.%JSONExport()
    }
    while rset.%Next(){
      write ","
      set department = ##class(osuwmc.Epic.Clarity.DepartmentMaster).%OpenId(rset.ID1)
      do department.%JSONExport()
    }
    write "]"
    quit tSC
}

ClassMethod GetEpicDepartment(departmentID As %String) As %Status
{
  #dim tSC as %Status = $$$OK
  #dim e As %Exception.AbstractException
  #dim id as %Integer

  set %response.ContentType = ..#CONTENTTYPEJSON
  &sql(SELECT ID1 INTO :id FROM osuwmc_Epic_Clarity.DepartmentMaster WHERE ID = :departmentID)
  IF SQLCODE<0 {WRITE "SQLCODE error ",SQLCODE," ",%msg  QUIT}
  ELSEIF SQLCODE=100 {WRITE "Query returns no results"  QUIT}
  set department = ##class(osuwmc.Epic.Clarity.DepartmentMaster).%OpenId(id)
  Do department.%JSONExport()
  QUIT tSC
}

ClassMethod SwaggerSpec() As %Status
{
  Set tSC = ##class(%REST.API).GetWebRESTApplication($NAMESPACE, %request.Application, .swagger)
  Do swagger.info.%Remove("x-ISC_Namespace")
  Set swagger.basePath = "/api/mgmnt/v1/TESTCLIN/spec/TableLookup"
  Set swagger.info.title = "REST API to Access and Query OSUWMC Cache Tables"
  Set swagger.info.version = "0.1"
  Set swagger.host = "intengtest"
  Return ..%ProcessResult($$$OK, swagger)
}

}

That helped. I was able to get my first two Method's called; however, I am struggling now with passing a value into the message.

<Routes> 
    <!-- Server Info -->
    <Route Url="/" Method="GET" Call="GetInfo" />
    <Route Url="/GetAllEpicDepartments" Method="GET" Call="GetAllEpicDepartments" />
    <Route Url="/GetEpicDepartment" Method="GET" Call="GetEpicDepartment" />
</Routes>

ClassMethod GetEpicDepartment(ID As %String) As %Status
{
    SET tSC = $$$OK
    set sql = "SELECT ID as DepartmentID, Abbr, Name, ExternalName, PhoneNumber, ApptPhone, FaxNumber, Address1, Address2, City, Zip, Specialty, RevLocID, RevLocName, BuildingCategoryID, BuildingName, DepCategoryTypeID, DepType, Center, EAFParent, CostCenter FROM osuwmc_Epic_Clarity.DepartmentMaster WHERE ID = ?"
    do ##class(%ZEN.Auxiliary.jsonSQLProvider).%WriteJSONFromSQL(,,sql,ID)
    return tSC
}

When I try to pass... https://intengtest/api/mgmnt/v1/TESTCLIN/spec/TableLookup/GetEpicDepartment/{ID} into postman I get the following...

{
    "errors": [
        {
            "code": 5002,
            "domain": "%ObjectErrors",
            "error": "ERROR #5002: ObjectScript error: <REGULAR EXPRESSION>PatternSet+4^%Regex.Matcher.1",
            "id": "ObjectScriptError",
            "params": [
                "&lt;REGULAR EXPRESSION&gt;PatternSet+4^%Regex.Matcher.1"
            ]
        }
    ],
    "summary": "ERROR #5002: ObjectScript error: &lt;REGULAR EXPRESSION&gt;PatternSet+4^%Regex.Matcher.1"
}